Mechanical compaction of insulator for insulated conductor splices

ABSTRACT

A method for coupling ends of two insulated conductors includes coupling an end portion of a core of a first insulated conductor to an end portion of a core of a second insulated conductor. At least a part of the end portions of the cores are at least partially exposed. Electrically insulating material is placed over the exposed portions of the cores. A sleeve is placed over end portions of the two insulated conductors to be coupled. The sleeve includes one or more raised portions. The end portions include the exposed portions of the cores. The sleeve is coupled to jackets of the insulated conductors. The raised portions of the sleeve are mechanically compressed until the raised portions of the sleeve have a diameter substantially similar to a remainder of the sleeve. The compression of the raised portions of the sleeve compacts the electrically insulating material inside the sleeve.

PRIORITY CLAIM

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 61/391,399 entitled “SYSTEMS AND METHODS FORJOINING INSULATED CONDUCTORS” to Coles et al. filed on Oct. 8, 2010; andU.S. Provisional Patent No. 61/473,594 entitled “SYSTEMS AND METHODS FORJOINING INSULATED CONDUCTORS” to Coles et al. filed on Apr. 8, 2011, allof which are incorporated by reference in their entirety.

RELATED PATENTS

This patent application incorporates by reference in its entirety eachof U.S. Pat. Nos. 6,688,387 to Wellington et al.; 6,991,036 toSumnu-Dindoruk et al.; 6,698,515 to Karanikas et al.; 6,880,633 toWellington et al.; 6,782,947 to de Rouffignac et al.; 6,991,045 toVinegar et al.; 7,073,578 to Vinegar et al.; 7,121,342 to Vinegar etal.; 7,320,364 to Fairbanks; 7,527,094 to McKinzie et al.; 7,584,789 toMo et al.; 7,533,719 to Hinson et al.; 7,562,707 to Miller; and7,798,220 to Vinegar et al.; U.S. Patent Application Publication Nos.2009-0189617 to Burns et al.; 2010-0071903 to Prince-Wright et al.;2010-0096137 to Nguyen et al.; and 2010-0258265 to Karanikas et al.

BACKGROUND

1. Field of the Invention

The present invention relates to systems for insulated conductors usedin heater elements. More particularly, the invention relates to fittingsto splice together insulated conductor cables.

2. Description of Related Art

Hydrocarbons obtained from subterranean formations are often used asenergy resources, as feedstocks, and as consumer products. Concerns overdepletion of available hydrocarbon resources and concerns over decliningoverall quality of produced hydrocarbons have led to development ofprocesses for more efficient recovery, processing and/or use ofavailable hydrocarbon resources. In situ processes may be used to removehydrocarbon materials from subterranean formations that were previouslyinaccessible and/or too expensive to extract using available methods.Chemical and/or physical properties of hydrocarbon material in asubterranean formation may need to be changed to allow hydrocarbonmaterial to be more easily removed from the subterranean formationand/or increase the value of the hydrocarbon material. The chemical andphysical changes may include in situ reactions that produce removablefluids, composition changes, solubility changes, density changes, phasechanges, and/or viscosity changes of the hydrocarbon material in theformation.

Heaters may be placed in wellbores to heat a formation during an in situprocess. There are many different types of heaters which may be used toheat the formation. Examples of in situ processes utilizing downholeheaters are illustrated in U.S. Pat. Nos. 2,634,961 to Ljungstrom;2,732,195 to Ljungstrom; 2,780,450 to Ljungstrom; 2,789,805 toLjungstrom; 2,923,535 to Ljungstrom; 4,886,118 to Van Meurs et al.; and6,688,387 to Wellington et al., each of which is incorporated byreference as if fully set forth herein.

Mineral insulated (MI) cables (insulated conductors) for use insubsurface applications, such as heating hydrocarbon containingformations in some applications, are longer, may have larger outsidediameters, and may operate at higher voltages and temperatures than whatis typical in the MI cable industry. There are many potential problemsduring manufacture and/or assembly of long length insulated conductors.

For example, there are potential electrical and/or mechanical problemsdue to degradation over time of the electrical insulator used in theinsulated conductor. There are also potential problems with electricalinsulators to overcome during assembly of the insulated conductorheater. Problems such as core bulge or other mechanical defects mayoccur during assembly of the insulated conductor heater. Suchoccurrences may lead to electrical problems during use of the heater andmay potentially render the heater inoperable for its intended purpose.

In addition, for subsurface applications, the joining of multiple MIcables may be needed to make MI cables with sufficient length to reachthe depths and distances needed to heat the subsurface efficiently andto join segments with different functions, such as lead-in cables joinedto heater sections. Such long heaters also require higher voltages toprovide enough power to the farthest ends of the heaters.

Conventional MI cable splice designs are typically not suitable forvoltages above 1000 volts, above 1500 volts, or above 2000 volts and maynot operate for extended periods without failure at elevatedtemperatures, such as over 650° C. (about 1200° F.), over 700° C. (about1290° F.), or over 800° C. (about 1470° F.). Such high voltage, hightemperature applications typically require the compaction of the mineralinsulant in the splice to be as close as possible to or above the levelof compaction in the insulated conductor (MI cable) itself.

The relatively large outside diameter and long length of MI cables forsome applications requires that the cables be spliced while orientedhorizontally. There are splices for other applications of MI cables thathave been fabricated horizontally. These techniques typically use asmall hole through which the mineral insulation (such as magnesium oxidepowder) is filled into the splice and compacted slightly throughvibration and tamping. Such methods do not provide sufficient compactionof the mineral insulation or even allow any compaction of the mineralinsulation, and are not suitable for making splices for use at the highvoltages needed for these subsurface applications.

Thus, there is a need for splices of insulated conductors that aresimple yet can operate at the high voltages and temperatures in thesubsurface environment over long durations without failure. In addition,the splices may need higher bending and tensile strengths to inhibitfailure of the splice under the weight loads and temperatures that thecables can be subjected to in the subsurface. Techniques and methodsalso may be utilized to reduce electric field intensities in the splicesso that leakage currents in the splices are reduced and to increase themargin between the operating voltage and electrical breakdown. Reducingelectric field intensities may help increase voltage and temperatureoperating ranges of the splices.

In addition, there may be problems with increased stress on theinsulated conductors during assembly and/or installation into thesubsurface of the insulated conductors. For example, winding andunwinding of the insulated conductors on spools used for transport andinstallation of the insulated conductors may lead to mechanical stresson the electrical insulators and/or other components in the insulatedconductors. Thus, more reliable systems and methods are needed to reduceor eliminate potential problems during manufacture, assembly, and/orinstallation of insulated conductors.

SUMMARY

Embodiments described herein generally relate to systems, methods, andheaters for treating a subsurface formation. Embodiments describedherein also generally relate to heaters that have novel componentstherein. Such heaters can be obtained by using the systems and methodsdescribed herein.

In certain embodiments, the invention provides one or more systems,methods, and/or heaters. In some embodiments, the systems, methods,and/or heaters are used for treating a subsurface formation.

In certain embodiments, a method for coupling ends of two insulatedconductors includes: coupling an end portion of a core of a firstinsulated conductor to an end portion of a core of a second insulatedconductor, wherein at least a part of the end portions of the cores areat least partially exposed; placing electrically insulating materialover the exposed portions of the cores; placing a sleeve over endportions of the two insulated conductors to be coupled, the sleevecomprising one or more raised portions, wherein the end portionscomprise the exposed portions of the cores; coupling the sleeve tojackets of the insulated conductors; and mechanically compressing theraised portions of the sleeve until the raised portions of the sleevehave a diameter substantially similar to a remainder of the sleeve,wherein the compression of the raised portions of the sleeve compactsthe electrically insulating material inside the sleeve.

In further embodiments, features from specific embodiments may becombined with features from other embodiments. For example, featuresfrom one embodiment may be combined with features from any of the otherembodiments.

In further embodiments, treating a subsurface formation is performedusing any of the methods, systems, power supplies, or heaters describedherein.

In further embodiments, additional features may be added to the specificembodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the methods and apparatus of the presentinvention will be more fully appreciated by reference to the followingdetailed description of presently preferred but nonetheless illustrativeembodiments in accordance with the present invention when taken inconjunction with the accompanying drawings.

FIG. 1 shows a schematic view of an embodiment of a portion of an insitu heat treatment system for treating a hydrocarbon containingformation.

FIG. 2 depicts an embodiment of an insulated conductor heat source.

FIG. 3 depicts an embodiment of an insulated conductor heat source.

FIG. 4 depicts an embodiment of an insulated conductor heat source.

FIG. 5 depicts a side view cross-sectional representation of oneembodiment of a fitting for joining insulated conductors.

FIG. 6 depicts an embodiment of a cutting tool.

FIG. 7 depicts a side view cross-sectional representation of anotherembodiment of a fitting for joining insulated conductors.

FIG. 8A depicts a side view of a cross-sectional representation of anembodiment of a threaded fitting for coupling three insulatedconductors.

FIG. 8B depicts a side view of a cross-sectional representation of anembodiment of a welded fitting for coupling three insulated conductors.

FIG. 9 depicts an embodiment of a torque tool.

FIG. 10 depicts an embodiment of a clamp assembly that may be used tocompact mechanically a fitting for joining insulated conductors.

FIG. 11 depicts an exploded view of an embodiment of a hydrauliccompaction machine.

FIG. 12 depicts a representation of an embodiment of an assembledhydraulic compaction machine.

FIG. 13 depicts an embodiment of a fitting and insulated conductorssecured in clamp assemblies before compaction of the fitting andinsulated conductors.

FIG. 14 depicts a side view representation of yet another embodiment ofa fitting for joining insulated conductors.

FIG. 15 depicts a side view representation of an embodiment of a fittingwith an opening covered with an insert.

FIG. 16 depicts an embodiment of a fitting with electric field reducingfeatures between the jackets of the insulated conductors and the sleevesand at the ends of the insulated conductors.

FIG. 17 depicts an embodiment of an electric field stress reducer.

FIG. 18 depicts a cross-sectional representation of a fitting asinsulated conductors are being moved into the fitting.

FIG. 19 depicts a cross-sectional representation of a fitting withinsulated conductors joined inside the fitting.

FIG. 20 depicts a cross-sectional representation of yet anotherembodiment of a fitting as insulated conductors are being moved into thefitting.

FIG. 21 depicts a cross-sectional representation of yet anotherembodiment of a fitting with insulated conductors joined inside thefitting.

FIG. 22 depicts an embodiment of blocks of electrically insulatingmaterial in position around cores of joined insulated conductors.

FIG. 23 depicts an embodiment of four blocks of electrically insulatingmaterial in position surrounding the cores of joined insulatedconductors.

FIG. 24 depicts an embodiment of an inner sleeve placed over joinedinsulated conductors.

FIG. 25 depicts an embodiment of an outer sleeve placed over an innersleeve and joined insulated conductors.

FIG. 26 depicts an embodiment of a chamfered end of an insulatedconductor after compression.

FIG. 27 depicts an embodiment of a first half of a compaction device tobe used for compaction of electrically insulating material at a couplingof insulated conductors.

FIG. 28 depicts an embodiment of a device coupled together aroundinsulated conductors.

FIG. 29 depicts a side view of an insulated conductor inside a devicewith a first plunger in position above the insulated conductor withexposed core.

FIG. 30 depicts a side view of an insulated conductor inside a devicewith a second plunger in position above the insulated conductor withexposed core.

FIGS. 31A-D depict other embodiments of a second plunger.

FIG. 32 depicts an embodiment with the second half of a device removedto leave the first half and electrically insulating material compactedaround the coupling between insulated conductors.

FIG. 33 depicts an embodiment of electrically insulating material shapedaround the coupling between insulated conductors.

FIG. 34 depicts an embodiment of a sleeve placed over electricallyinsulating material.

FIG. 35 depicts a representation of an embodiment of a hydraulic pressmachine that may be used to apply force to a plunger to hydraulicallycompact electrically insulating material inside a device.

FIG. 36 depicts an embodiment of a sleeve that is used incircumferential mechanical compression.

FIG. 37 depicts an embodiment of a sleeve on insulated conductors afterthe sleeve and ribs have been circumferentially compressed.

FIG. 38 depicts an embodiment of reinforcement sleeves on joinedinsulated conductors.

FIG. 39 depicts an exploded view of another embodiment of a fitting usedfor coupling three insulated conductors.

FIGS. 40-47 depict an embodiment of a method for installation of afitting onto ends of insulated conductors.

FIG. 48 depicts an embodiment of a compaction tool that can be used tocompact electrically insulating material.

FIG. 49 depicts an embodiment of another compaction tool that can beused to compact electrically insulating material.

FIG. 50 depicts an embodiment of a compaction tool that can be used forthe final compaction of electrically insulating material.

While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Thedrawings may not be to scale. It should be understood that the drawingsand detailed description thereto are not intended to limit the inventionto the particular form disclosed, but to the contrary, the intention isto cover all modifications, equivalents and alternatives falling withinthe spirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION

The following description generally relates to systems and methods fortreating hydrocarbons in the formations. Such formations may be treatedto yield hydrocarbon products, hydrogen, and other products.

“Alternating current (AC)” refers to a time-varying current thatreverses direction substantially sinusoidally. AC produces skin effectelectricity flow in a ferromagnetic conductor.

“Coupled” means either a direct connection or an indirect connection(for example, one or more intervening connections) between one or moreobjects or components. The phrase “directly connected” means a directconnection between objects or components such that the objects orcomponents are connected directly to each other so that the objects orcomponents operate in a “point of use” manner.

A “formation” includes one or more hydrocarbon containing layers, one ormore non-hydrocarbon layers, an overburden, and/or an underburden.“Hydrocarbon layers” refer to layers in the formation that containhydrocarbons. The hydrocarbon layers may contain non-hydrocarbonmaterial and hydrocarbon material. The “overburden” and/or the“underburden” include one or more different types of impermeablematerials. For example, the overburden and/or underburden may includerock, shale, mudstone, or wet/tight carbonate. In some embodiments of insitu heat treatment processes, the overburden and/or the underburden mayinclude a hydrocarbon containing layer or hydrocarbon containing layersthat are relatively impermeable and are not subjected to temperaturesduring in situ heat treatment processing that result in significantcharacteristic changes of the hydrocarbon containing layers of theoverburden and/or the underburden. For example, the underburden maycontain shale or mudstone, but the underburden is not allowed to heat topyrolysis temperatures during the in situ heat treatment process. Insome cases, the overburden and/or the underburden may be somewhatpermeable.

“Formation fluids” refer to fluids present in a formation and mayinclude pyrolyzation fluid, synthesis gas, mobilized hydrocarbons, andwater (steam). Formation fluids may include hydrocarbon fluids as wellas non-hydrocarbon fluids. The term “mobilized fluid” refers to fluidsin a hydrocarbon containing formation that are able to flow as a resultof thermal treatment of the formation. “Produced fluids” refer to fluidsremoved from the formation.

A “heat source” is any system for providing heat to at least a portionof a formation substantially by conductive and/or radiative heattransfer. For example, a heat source may include electrically conductingmaterials and/or electric heaters such as an insulated conductor, anelongated member, and/or a conductor disposed in a conduit. A heatsource may also include systems that generate heat by burning a fuelexternal to or in a formation. The systems may be surface burners,downhole gas burners, flameless distributed combustors, and naturaldistributed combustors. In some embodiments, heat provided to orgenerated in one or more heat sources may be supplied by other sourcesof energy. The other sources of energy may directly heat a formation, orthe energy may be applied to a transfer medium that directly orindirectly heats the formation. It is to be understood that one or moreheat sources that are applying heat to a formation may use differentsources of energy. Thus, for example, for a given formation some heatsources may supply heat from electrically conducting materials, electricresistance heaters, some heat sources may provide heat from combustion,and some heat sources may provide heat from one or more other energysources (for example, chemical reactions, solar energy, wind energy,biomass, or other sources of renewable energy). A chemical reaction mayinclude an exothermic reaction (for example, an oxidation reaction). Aheat source may also include an electrically conducting material and/ora heater that provides heat to a zone proximate and/or surrounding aheating location such as a heater well.

A “heater” is any system or heat source for generating heat in a well ora near wellbore region. Heaters may be, but are not limited to, electricheaters, burners, combustors that react with material in or producedfrom a formation, and/or combinations thereof.

“Hydrocarbons” are generally defined as molecules formed primarily bycarbon and hydrogen atoms. Hydrocarbons may also include other elementssuch as, but not limited to, halogens, metallic elements, nitrogen,oxygen, and/or sulfur. Hydrocarbons may be, but are not limited to,kerogen, bitumen, pyrobitumen, oils, natural mineral waxes, andasphaltites. Hydrocarbons may be located in or adjacent to mineralmatrices in the earth. Matrices may include, but are not limited to,sedimentary rock, sands, silicilytes, carbonates, diatomites, and otherporous media. “Hydrocarbon fluids” are fluids that include hydrocarbons.Hydrocarbon fluids may include, entrain, or be entrained innon-hydrocarbon fluids such as hydrogen, nitrogen, carbon monoxide,carbon dioxide, hydrogen sulfide, water, and ammonia.

An “in situ conversion process” refers to a process of heating ahydrocarbon containing formation from heat sources to raise thetemperature of at least a portion of the formation above a pyrolysistemperature so that pyrolyzation fluid is produced in the formation.

An “in situ heat treatment process” refers to a process of heating ahydrocarbon containing formation with heat sources to raise thetemperature of at least a portion of the formation above a temperaturethat results in mobilized fluid, visbreaking, and/or pyrolysis ofhydrocarbon containing material so that mobilized fluids, visbrokenfluids, and/or pyrolyzation fluids are produced in the formation.

“Insulated conductor” refers to any elongated material that is able toconduct electricity and that is covered, in whole or in part, by anelectrically insulating material.

“Nitride” refers to a compound of nitrogen and one or more otherelements of the Periodic Table. Nitrides include, but are not limitedto, silicon nitride, boron nitride, or alumina nitride.

“Perforations” include openings, slits, apertures, or holes in a wall ofa conduit, tubular, pipe or other flow pathway that allow flow into orout of the conduit, tubular, pipe or other flow pathway.

“Pyrolysis” is the breaking of chemical bonds due to the application ofheat. For example, pyrolysis may include transforming a compound intoone or more other substances by heat alone. Heat may be transferred to asection of the formation to cause pyrolysis.

“Pyrolyzation fluids” or “pyrolysis products” refers to fluid producedsubstantially during pyrolysis of hydrocarbons. Fluid produced bypyrolysis reactions may mix with other fluids in a formation. Themixture would be considered pyrolyzation fluid or pyrolyzation product.As used herein, “pyrolysis zone” refers to a volume of a formation (forexample, a relatively permeable formation such as a tar sands formation)that is reacted or reacting to form a pyrolyzation fluid.

“Thickness” of a layer refers to the thickness of a cross section of thelayer, wherein the cross section is normal to a face of the layer.

The term “wellbore” refers to a hole in a formation made by drilling orinsertion of a conduit into the formation. A wellbore may have asubstantially circular cross section, or another cross-sectional shape.As used herein, the terms “well” and “opening,” when referring to anopening in the formation may be used interchangeably with the term“wellbore.”

A formation may be treated in various ways to produce many differentproducts. Different stages or processes may be used to treat theformation during an in situ heat treatment process. In some embodiments,one or more sections of the formation are solution mined to removesoluble minerals from the sections. Solution mining minerals may beperformed before, during, and/or after the in situ heat treatmentprocess. In some embodiments, the average temperature of one or moresections being solution mined may be maintained below about 120° C.

In some embodiments, one or more sections of the formation are heated toremove water from the sections and/or to remove methane and othervolatile hydrocarbons from the sections. In some embodiments, theaverage temperature may be raised from ambient temperature totemperatures below about 220° C. during removal of water and volatilehydrocarbons.

In some embodiments, one or more sections of the formation are heated totemperatures that allow for movement and/or visbreaking of hydrocarbonsin the formation. In some embodiments, the average temperature of one ormore sections of the formation are raised to mobilization temperaturesof hydrocarbons in the sections (for example, to temperatures rangingfrom 100° C. to 250° C., from 120° C. to 240° C., or from 150° C. to230° C.).

In some embodiments, one or more sections are heated to temperaturesthat allow for pyrolysis reactions in the formation. In someembodiments, the average temperature of one or more sections of theformation may be raised to pyrolysis temperatures of hydrocarbons in thesections (for example, temperatures ranging from 230° C. to 900° C.,from 240° C. to 400° C. or from 250° C. to 350° C.).

Heating the hydrocarbon containing formation with a plurality of heatsources may establish thermal gradients around the heat sources thatraise the temperature of hydrocarbons in the formation to desiredtemperatures at desired heating rates. The rate of temperature increasethrough the mobilization temperature range and/or the pyrolysistemperature range for desired products may affect the quality andquantity of the formation fluids produced from the hydrocarboncontaining formation. Slowly raising the temperature of the formationthrough the mobilization temperature range and/or pyrolysis temperaturerange may allow for the production of high quality, high API gravityhydrocarbons from the formation. Slowly raising the temperature of theformation through the mobilization temperature range and/or pyrolysistemperature range may allow for the removal of a large amount of thehydrocarbons present in the formation as hydrocarbon product.

In some in situ heat treatment embodiments, a portion of the formationis heated to a desired temperature instead of slowly heating thetemperature through a temperature range. In some embodiments, thedesired temperature is 300° C., 325° C., or 350° C. Other temperaturesmay be selected as the desired temperature.

Superposition of heat from heat sources allows the desired temperatureto be relatively quickly and efficiently established in the formation.Energy input into the formation from the heat sources may be adjusted tomaintain the temperature in the formation substantially at a desiredtemperature.

Mobilization and/or pyrolysis products may be produced from theformation through production wells. In some embodiments, the averagetemperature of one or more sections is raised to mobilizationtemperatures and hydrocarbons are produced from the production wells.The average temperature of one or more of the sections may be raised topyrolysis temperatures after production due to mobilization decreasesbelow a selected value. In some embodiments, the average temperature ofone or more sections may be raised to pyrolysis temperatures withoutsignificant production before reaching pyrolysis temperatures. Formationfluids including pyrolysis products may be produced through theproduction wells.

In some embodiments, the average temperature of one or more sections maybe raised to temperatures sufficient to allow synthesis gas productionafter mobilization and/or pyrolysis. In some embodiments, hydrocarbonsmay be raised to temperatures sufficient to allow synthesis gasproduction without significant production before reaching thetemperatures sufficient to allow synthesis gas production. For example,synthesis gas may be produced in a temperature range from about 400° C.to about 1200° C., about 500° C. to about 1100° C., or about 550° C. toabout 1000° C. A synthesis gas generating fluid (for example, steamand/or water) may be introduced into the sections to generate synthesisgas. Synthesis gas may be produced from production wells.

Solution mining, removal of volatile hydrocarbons and water, mobilizinghydrocarbons, pyrolyzing hydrocarbons, generating synthesis gas, and/orother processes may be performed during the in situ heat treatmentprocess. In some embodiments, some processes may be performed after thein situ heat treatment process. Such processes may include, but are notlimited to, recovering heat from treated sections, storing fluids (forexample, water and/or hydrocarbons) in previously treated sections,and/or sequestering carbon dioxide in previously treated sections.

FIG. 1 depicts a schematic view of an embodiment of a portion of the insitu heat treatment system for treating the hydrocarbon containingformation. The in situ heat treatment system may include barrier wells200. Barrier wells are used to form a barrier around a treatment area.The barrier inhibits fluid flow into and/or out of the treatment area.Barrier wells include, but are not limited to, dewatering wells, vacuumwells, capture wells, injection wells, grout wells, freeze wells, orcombinations thereof. In some embodiments, barrier wells 200 aredewatering wells. Dewatering wells may remove liquid water and/orinhibit liquid water from entering a portion of the formation to beheated, or to the formation being heated. In the embodiment depicted inFIG. 1, the barrier wells 200 are shown extending only along one side ofheat sources 202, but the barrier wells typically encircle all heatsources 202 used, or to be used, to heat a treatment area of theformation.

Heat sources 202 are placed in at least a portion of the formation. Heatsources 202 may include heaters such as insulated conductors,conductor-in-conduit heaters, surface burners, flameless distributedcombustors, and/or natural distributed combustors. Heat sources 202 mayalso include other types of heaters. Heat sources 202 provide heat to atleast a portion of the formation to heat hydrocarbons in the formation.Energy may be supplied to heat sources 202 through supply lines 204.Supply lines 204 may be structurally different depending on the type ofheat source or heat sources used to heat the formation. Supply lines 204for heat sources may transmit electricity for electric heaters, maytransport fuel for combustors, or may transport heat exchange fluid thatis circulated in the formation. In some embodiments, electricity for anin situ heat treatment process may be provided by a nuclear power plantor nuclear power plants. The use of nuclear power may allow forreduction or elimination of carbon dioxide emissions from the in situheat treatment process.

When the formation is heated, the heat input into the formation maycause expansion of the formation and geomechanical motion. The heatsources may be turned on before, at the same time, or during adewatering process. Computer simulations may model formation response toheating. The computer simulations may be used to develop a pattern andtime sequence for activating heat sources in the formation so thatgeomechanical motion of the formation does not adversely affect thefunctionality of heat sources, production wells, and other equipment inthe formation.

Heating the formation may cause an increase in permeability and/orporosity of the formation. Increases in permeability and/or porosity mayresult from a reduction of mass in the formation due to vaporization andremoval of water, removal of hydrocarbons, and/or creation of fractures.Fluid may flow more easily in the heated portion of the formationbecause of the increased permeability and/or porosity of the formation.Fluid in the heated portion of the formation may move a considerabledistance through the formation because of the increased permeabilityand/or porosity. The considerable distance may be over 1000 m dependingon various factors, such as permeability of the formation, properties ofthe fluid, temperature of the formation, and pressure gradient allowingmovement of the fluid. The ability of fluid to travel considerabledistance in the formation allows production wells 206 to be spacedrelatively far apart in the formation.

Production wells 206 are used to remove formation fluid from theformation. In some embodiments, production well 206 includes a heatsource. The heat source in the production well may heat one or moreportions of the formation at or near the production well. In some insitu heat treatment process embodiments, the amount of heat supplied tothe formation from the production well per meter of the production wellis less than the amount of heat applied to the formation from a heatsource that heats the formation per meter of the heat source. Heatapplied to the formation from the production well may increase formationpermeability adjacent to the production well by vaporizing and removingliquid phase fluid adjacent to the production well and/or by increasingthe permeability of the formation adjacent to the production well byformation of macro and/or micro fractures.

More than one heat source may be positioned in the production well. Aheat source in a lower portion of the production well may be turned offwhen superposition of heat from adjacent heat sources heats theformation sufficiently to counteract benefits provided by heating theformation with the production well. In some embodiments, the heat sourcein an upper portion of the production well may remain on after the heatsource in the lower portion of the production well is deactivated. Theheat source in the upper portion of the well may inhibit condensationand reflux of formation fluid.

In some embodiments, the heat source in production well 206 allows forvapor phase removal of formation fluids from the formation. Providingheating at or through the production well may: (1) inhibit condensationand/or refluxing of production fluid when such production fluid ismoving in the production well proximate the overburden, (2) increaseheat input into the formation, (3) increase production rate from theproduction well as compared to a production well without a heat source,(4) inhibit condensation of high carbon number compounds (C6hydrocarbons and above) in the production well, and/or (5) increaseformation permeability at or proximate the production well.

Subsurface pressure in the formation may correspond to the fluidpressure generated in the formation. As temperatures in the heatedportion of the formation increase, the pressure in the heated portionmay increase as a result of thermal expansion of in situ fluids,increased fluid generation and vaporization of water. Controlling rateof fluid removal from the formation may allow for control of pressure inthe formation. Pressure in the formation may be determined at a numberof different locations, such as near or at production wells, near or atheat sources, or at monitor wells.

In some hydrocarbon containing formations, production of hydrocarbonsfrom the formation is inhibited until at least some hydrocarbons in theformation have been mobilized and/or pyrolyzed. Formation fluid may beproduced from the formation when the formation fluid is of a selectedquality. In some embodiments, the selected quality includes an APIgravity of at least about 20°, 30°, or 40°. Inhibiting production untilat least some hydrocarbons are mobilized and/or pyrolyzed may increaseconversion of heavy hydrocarbons to light hydrocarbons. Inhibitinginitial production may minimize the production of heavy hydrocarbonsfrom the formation. Production of substantial amounts of heavyhydrocarbons may require expensive equipment and/or reduce the life ofproduction equipment.

In some hydrocarbon containing formations, hydrocarbons in the formationmay be heated to mobilization and/or pyrolysis temperatures beforesubstantial permeability has been generated in the heated portion of theformation. An initial lack of permeability may inhibit the transport ofgenerated fluids to production wells 206. During initial heating, fluidpressure in the formation may increase proximate heat sources 202. Theincreased fluid pressure may be released, monitored, altered, and/orcontrolled through one or more heat sources 202. For example, selectedheat sources 202 or separate pressure relief wells may include pressurerelief valves that allow for removal of some fluid from the formation.

In some embodiments, pressure generated by expansion of mobilizedfluids, pyrolysis fluids or other fluids generated in the formation maybe allowed to increase although an open path to production wells 206 orany other pressure sink may not yet exist in the formation. The fluidpressure may be allowed to increase towards a lithostatic pressure.Fractures in the hydrocarbon containing formation may form when thefluid approaches the lithostatic pressure. For example, fractures mayform from heat sources 202 to production wells 206 in the heated portionof the formation. The generation of fractures in the heated portion mayrelieve some of the pressure in the portion. Pressure in the formationmay have to be maintained below a selected pressure to inhibit unwantedproduction, fracturing of the overburden or underburden, and/or cokingof hydrocarbons in the formation.

After mobilization and/or pyrolysis temperatures are reached andproduction from the formation is allowed, pressure in the formation maybe varied to alter and/or control a composition of formation fluidproduced, to control a percentage of condensable fluid as compared tonon-condensable fluid in the formation fluid, and/or to control an APIgravity of formation fluid being produced. For example, decreasingpressure may result in production of a larger condensable fluidcomponent. The condensable fluid component may contain a largerpercentage of olefins.

In some in situ heat treatment process embodiments, pressure in theformation may be maintained high enough to promote production offormation fluid with an API gravity of greater than 20°. Maintainingincreased pressure in the formation may inhibit formation subsidenceduring in situ heat treatment. Maintaining increased pressure may reduceor eliminate the need to compress formation fluids at the surface totransport the fluids in collection conduits to treatment facilities.

Maintaining increased pressure in a heated portion of the formation maysurprisingly allow for production of large quantities of hydrocarbons ofincreased quality and of relatively low molecular weight. Pressure maybe maintained so that formation fluid produced has a minimal amount ofcompounds above a selected carbon number. The selected carbon number maybe at most 25, at most 20, at most 12, or at most 8. Some high carbonnumber compounds may be entrained in vapor in the formation and may beremoved from the formation with the vapor. Maintaining increasedpressure in the formation may inhibit entrainment of high carbon numbercompounds and/or multi-ring hydrocarbon compounds in the vapor. Highcarbon number compounds and/or multi-ring hydrocarbon compounds mayremain in a liquid phase in the formation for significant time periods.The significant time periods may provide sufficient time for thecompounds to pyrolyze to form lower carbon number compounds.

Generation of relatively low molecular weight hydrocarbons is believedto be due, in part, to autogenous generation and reaction of hydrogen ina portion of the hydrocarbon containing formation. For example,maintaining an increased pressure may force hydrogen generated duringpyrolysis into the liquid phase within the formation. Heating theportion to a temperature in a pyrolysis temperature range may pyrolyzehydrocarbons in the formation to generate liquid phase pyrolyzationfluids. The generated liquid phase pyrolyzation fluids components mayinclude double bonds and/or radicals. Hydrogen (H₂) in the liquid phasemay reduce double bonds of the generated pyrolyzation fluids, therebyreducing a potential for polymerization or formation of long chaincompounds from the generated pyrolyzation fluids. In addition, H₂ mayalso neutralize radicals in the generated pyrolyzation fluids. H₂ in theliquid phase may inhibit the generated pyrolyzation fluids from reactingwith each other and/or with other compounds in the formation.

Formation fluid produced from production wells 206 may be transportedthrough collection piping 208 to treatment facilities 210. Formationfluids may also be produced from heat sources 202. For example, fluidmay be produced from heat sources 202 to control pressure in theformation adjacent to the heat sources. Fluid produced from heat sources202 may be transported through tubing or piping to collection piping 208or the produced fluid may be transported through tubing or pipingdirectly to treatment facilities 210. Treatment facilities 210 mayinclude separation units, reaction units, upgrading units, fuel cells,turbines, storage vessels, and/or other systems and units for processingproduced formation fluids. The treatment facilities may formtransportation fuel from at least a portion of the hydrocarbons producedfrom the formation. In some embodiments, the transportation fuel may bejet fuel, such as JP-8.

An insulated conductor may be used as an electric heater element of aheater or a heat source. The insulated conductor may include an innerelectrical conductor (core) surrounded by an electrical insulator and anouter electrical conductor (jacket). The electrical insulator mayinclude mineral insulation (for example, magnesium oxide) or otherelectrical insulation.

In certain embodiments, the insulated conductor is placed in an openingin a hydrocarbon containing formation. In some embodiments, theinsulated conductor is placed in an uncased opening in the hydrocarboncontaining formation. Placing the insulated conductor in an uncasedopening in the hydrocarbon containing formation may allow heat transferfrom the insulated conductor to the formation by radiation as well asconduction. Using an uncased opening may facilitate retrieval of theinsulated conductor from the well, if necessary.

In some embodiments, an insulated conductor is placed within a casing inthe formation; may be cemented within the formation; or may be packed inan opening with sand, gravel, or other fill material. The insulatedconductor may be supported on a support member positioned within theopening. The support member may be a cable, rod, or a conduit (forexample, a pipe). The support member may be made of a metal, ceramic,inorganic material, or combinations thereof. Because portions of asupport member may be exposed to formation fluids and heat during use,the support member may be chemically resistant and/or thermallyresistant.

Ties, spot welds, and/or other types of connectors may be used to couplethe insulated conductor to the support member at various locations alonga length of the insulated conductor. The support member may be attachedto a wellhead at an upper surface of the formation. In some embodiments,the insulated conductor has sufficient structural strength such that asupport member is not needed. The insulated conductor may, in manyinstances, have at least some flexibility to inhibit thermal expansiondamage when undergoing temperature changes.

In certain embodiments, insulated conductors are placed in wellboreswithout support members and/or centralizers. An insulated conductorwithout support members and/or centralizers may have a suitablecombination of temperature and corrosion resistance, creep strength,length, thickness (diameter), and metallurgy that will inhibit failureof the insulated conductor during use.

FIG. 2 depicts a perspective view of an end portion of an embodiment ofinsulated conductor 212. Insulated conductor 212 may have any desiredcross-sectional shape such as, but not limited to, round (depicted inFIG. 2), triangular, ellipsoidal, rectangular, hexagonal, or irregular.In certain embodiments, insulated conductor 212 includes core 214,electrical insulator 216, and jacket 218. Core 214 may resistively heatwhen an electrical current passes through the core. Alternating ortime-varying current and/or direct current may be used to provide powerto core 214 such that the core resistively heats.

In some embodiments, electrical insulator 216 inhibits current leakageand arcing to jacket 218. Electrical insulator 216 may thermally conductheat generated in core 214 to jacket 218. Jacket 218 may radiate orconduct heat to the formation. In certain embodiments, insulatedconductor 212 is 1000 m or more in length. Longer or shorter insulatedconductors may also be used to meet specific application needs. Thedimensions of core 214, electrical insulator 216, and jacket 218 ofinsulated conductor 212 may be selected such that the insulatedconductor has enough strength to be self supporting even at upperworking temperature limits. Such insulated conductors may be suspendedfrom wellheads or supports positioned near an interface between anoverburden and a hydrocarbon containing formation without the need forsupport members extending into the hydrocarbon containing formationalong with the insulated conductors.

Insulated conductor 212 may be designed to operate at power levels of upto about 1650 watts/meter or higher. In certain embodiments, insulatedconductor 212 operates at a power level between about 500 watts/meterand about 1150 watts/meter when heating a formation. Insulated conductor212 may be designed so that a maximum voltage level at a typicaloperating temperature does not cause substantial thermal and/orelectrical breakdown of electrical insulator 216. Insulated conductor212 may be designed such that jacket 218 does not exceed a temperaturethat will result in a significant reduction in corrosion resistanceproperties of the jacket material. In certain embodiments, insulatedconductor 212 may be designed to reach temperatures within a rangebetween about 650° C. and about 900° C. Insulated conductors havingother operating ranges may be formed to meet specific operationalrequirements.

FIG. 2 depicts insulated conductor 212 having a single core 214. In someembodiments, insulated conductor 212 has two or more cores 214. Forexample, a single insulated conductor may have three cores. Core 214 maybe made of metal or another electrically conductive material. Thematerial used to form core 214 may include, but not be limited to,nichrome, copper, nickel, carbon steel, stainless steel, andcombinations thereof. In certain embodiments, core 214 is chosen to havea diameter and a resistivity at operating temperatures such that itsresistance, as derived from Ohm's law, makes it electrically andstructurally stable for the chosen power dissipation per meter, thelength of the heater, and/or the maximum voltage allowed for the corematerial.

In some embodiments, core 214 is made of different materials along alength of insulated conductor 212. For example, a first section of core214 may be made of a material that has a significantly lower resistancethan a second section of the core. The first section may be placedadjacent to a formation layer that does not need to be heated to as higha temperature as a second formation layer that is adjacent to the secondsection. The resistivity of various sections of core 214 may be adjustedby having a variable diameter and/or by having core sections made ofdifferent materials.

Electrical insulator 216 may be made of a variety of materials. Commonlyused powders may include, but are not limited to, MgO, Al₂O₃, Zirconia,BeO, different chemical variations of Spinels, and combinations thereof.MgO may provide good thermal conductivity and electrical insulationproperties. The desired electrical insulation properties include lowleakage current and high dielectric strength. A low leakage currentdecreases the possibility of thermal breakdown and the high dielectricstrength decreases the possibility of arcing across the insulator.Thermal breakdown can occur if the leakage current causes a progressiverise in the temperature of the insulator leading also to arcing acrossthe insulator.

Jacket 218 may be an outer metallic layer or electrically conductivelayer. Jacket 218 may be in contact with hot formation fluids. Jacket218 may be made of material having a high resistance to corrosion atelevated temperatures. Alloys that may be used in a desired operatingtemperature range of jacket 218 include, but are not limited to, 304stainless steel, 310 stainless steel, Incoloy® 800, and Inconel® 600(Inco Alloys International, Huntington, W. Va., U.S.A.). The thicknessof jacket 218 may have to be sufficient to last for three to ten yearsin a hot and corrosive environment. A thickness of jacket 218 maygenerally vary between about 1 mm and about 2.5 mm. For example, a 1.3mm thick, 310 stainless steel outer layer may be used as jacket 218 toprovide good chemical resistance to sulfidation corrosion in a heatedzone of a formation for a period of over 3 years. Larger or smallerjacket thicknesses may be used to meet specific applicationrequirements.

One or more insulated conductors may be placed within an opening in aformation to form a heat source or heat sources. Electrical current maybe passed through each insulated conductor in the opening to heat theformation. Alternately, electrical current may be passed throughselected insulated conductors in an opening. The unused conductors maybe used as backup heaters. Insulated conductors may be electricallycoupled to a power source in any convenient manner. Each end of aninsulated conductor may be coupled to lead-in cables that pass through awellhead. Such a configuration typically has a 180° bend (a “hairpin”bend) or turn located near a bottom of the heat source. An insulatedconductor that includes a 180° bend or turn may not require a bottomtermination, but the 180° bend or turn may be an electrical and/orstructural weakness in the heater. Insulated conductors may beelectrically coupled together in series, in parallel, or in series andparallel combinations. In some embodiments of heat sources, electricalcurrent may pass into the conductor of an insulated conductor and may bereturned through the jacket of the insulated conductor by connectingcore 214 to jacket 218 (shown in FIG. 2) at the bottom of the heatsource.

In some embodiments, three insulated conductors 212 are electricallycoupled in a 3-phase wye configuration to a power supply. FIG. 3 depictsan embodiment of three insulated conductors in an opening in asubsurface formation coupled in a wye configuration. FIG. 4 depicts anembodiment of three insulated conductors 212 that are removable fromopening 220 in the formation. No bottom connection may be required forthree insulated conductors in a wye configuration. Alternately, allthree insulated conductors of the wye configuration may be connectedtogether near the bottom of the opening. The connection may be madedirectly at ends of heating sections of the insulated conductors or atends of cold pins (less resistive sections) coupled to the heatingsections at the bottom of the insulated conductors. The bottomconnections may be made with insulator filled and sealed canisters orwith epoxy filled canisters. The insulator may be the same compositionas the insulator used as the electrical insulation.

Three insulated conductors 212 depicted in FIGS. 3 and 4 may be coupledto support member 222 using centralizers 224. Alternatively, insulatedconductors 212 may be strapped directly to support member 222 usingmetal straps. Centralizers 224 may maintain a location and/or inhibitmovement of insulated conductors 212 on support member 222. Centralizers224 may be made of metal, ceramic, or combinations thereof. The metalmay be stainless steel or any other type of metal able to withstand acorrosive and high temperature environment. In some embodiments,centralizers 224 are bowed metal strips welded to the support member atdistances less than about 6 m. A ceramic used in centralizer 224 may be,but is not limited to, Al₂O₃, MgO, or another electrical insulator.Centralizers 224 may maintain a location of insulated conductors 212 onsupport member 222 such that movement of insulated conductors isinhibited at operating temperatures of the insulated conductors.Insulated conductors 212 may also be somewhat flexible to withstandexpansion of support member 222 during heating.

Support member 222, insulated conductor 212, and centralizers 224 may beplaced in opening 220 in hydrocarbon layer 226. Insulated conductors 212may be coupled to bottom conductor junction 228 using cold pin 230.Bottom conductor junction 228 may electrically couple each insulatedconductor 212 to each other. Bottom conductor junction 228 may includematerials that are electrically conducting and do not melt attemperatures found in opening 220. Cold pin 230 may be an insulatedconductor having lower electrical resistance than insulated conductor212.

Lead-in conductor 232 may be coupled to wellhead 234 to provideelectrical power to insulated conductor 212. Lead-in conductor 232 maybe made of a relatively low electrical resistance conductor such thatrelatively little heat is generated from electrical current passingthrough the lead-in conductor. In some embodiments, the lead-inconductor is a rubber or polymer insulated stranded copper wire. In someembodiments, the lead-in conductor is a mineral insulated conductor witha copper core. Lead-in conductor 232 may couple to wellhead 234 atsurface 236 through a sealing flange located between overburden 238 andsurface 236. The sealing flange may inhibit fluid from escaping fromopening 220 to surface 236.

In certain embodiments, lead-in conductor 232 is coupled to insulatedconductor 212 using transition conductor 240. Transition conductor 240may be a less resistive portion of insulated conductor 212. Transitionconductor 240 may be referred to as “cold pin” of insulated conductor212. Transition conductor 240 may be designed to dissipate aboutone-tenth to about one-fifth of the power per unit length as isdissipated in a unit length of the primary heating section of insulatedconductor 212. Transition conductor 240 may typically be between about1.5 m and about 15 m, although shorter or longer lengths may be used toaccommodate specific application needs. In an embodiment, the conductorof transition conductor 240 is copper. The electrical insulator oftransition conductor 240 may be the same type of electrical insulatorused in the primary heating section. A jacket of transition conductor240 may be made of corrosion resistant material.

In certain embodiments, transition conductor 240 is coupled to lead-inconductor 232 by a splice or other coupling joint. Splices may also beused to couple transition conductor 240 to insulated conductor 212.Splices may have to withstand a temperature equal to half of a targetzone operating temperature. Density of electrical insulation in thesplice should in many instances be high enough to withstand the requiredtemperature and the operating voltage.

In some embodiments, as shown in FIG. 3, packing material 242 is placedbetween overburden casing 244 and opening 220. In some embodiments,reinforcing material 246 may secure overburden casing 244 to overburden238. Packing material 242 may inhibit fluid from flowing from opening220 to surface 236. Reinforcing material 246 may include, for example,Class G or Class H Portland cement mixed with silica flour for improvedhigh temperature performance, slag or silica flour, and/or a mixturethereof. In some embodiments, reinforcing material 246 extends radiallya width of from about 5 cm to about 25 cm.

As shown in FIGS. 3 and 4, support member 222 and lead-in conductor 232may be coupled to wellhead 234 at surface 236 of the formation. Surfaceconductor 248 may enclose reinforcing material 246 and couple towellhead 234. Embodiments of surface conductors may extend to depths ofapproximately 3 m to approximately 515 m into an opening in theformation. Alternatively, the surface conductor may extend to a depth ofapproximately 9 m into the formation. Electrical current may be suppliedfrom a power source to insulated conductor 212 to generate heat due tothe electrical resistance of the insulated conductor. Heat generatedfrom three insulated conductors 212 may transfer within opening 220 toheat at least a portion of hydrocarbon layer 226.

Heat generated by insulated conductors 212 may heat at least a portionof a hydrocarbon containing formation. In some embodiments, heat istransferred to the formation substantially by radiation of the generatedheat to the formation. Some heat may be transferred by conduction orconvection of heat due to gases present in the opening. The opening maybe an uncased opening, as shown in FIGS. 3 and 4. An uncased openingeliminates cost associated with thermally cementing the heater to theformation, costs associated with a casing, and/or costs of packing aheater within an opening. In addition, heat transfer by radiation istypically more efficient than by conduction, so the heaters may beoperated at lower temperatures in an open wellbore. Conductive heattransfer during initial operation of a heat source may be enhanced bythe addition of a gas in the opening. The gas may be maintained at apressure up to about 27 bars absolute. The gas may include, but is notlimited to, carbon dioxide and/or helium. An insulated conductor heaterin an open wellbore may advantageously be free to expand or contract toaccommodate thermal expansion and contraction. An insulated conductorheater may advantageously be removable or redeployable from an openwellbore.

In certain embodiments, an insulated conductor heater assembly isinstalled or removed using a spooling assembly. More than one spoolingassembly may be used to install both the insulated conductor and asupport member simultaneously. Alternatively, the support member may beinstalled using a coiled tubing unit. The heaters may be un-spooled andconnected to the support as the support is inserted into the well. Theelectric heater and the support member may be un-spooled from thespooling assemblies. Spacers may be coupled to the support member andthe heater along a length of the support member. Additional spoolingassemblies may be used for additional electric heater elements.

Temperature limited heaters may be in configurations and/or may includematerials that provide automatic temperature limiting properties for theheater at certain temperatures. Examples of temperature limited heatersmay be found in U.S. Pat. Nos. 6,688,387 to Wellington et al.; 6,991,036to Sumnu-Dindoruk et al.; 6,698,515 to Karanikas et al.; 6,880,633 toWellington et al.; 6,782,947 to de Rouffignac et al.; 6,991,045 toVinegar et al.; 7,073,578 to Vinegar et al.; 7,121,342 to Vinegar etal.; 7,320,364 to Fairbanks; 7,527,094 to McKinzie et al.; 7,584,789 toMo et al.; 7,533,719 to Hinson et al.; and 7,562,707 to Miller; U.S.Patent Application Publication Nos. 2009-0071652 to Vinegar et al.;2009-0189617 to Burns et al.; 2010-0071903 to Prince-Wright et al.; and2010-0096137 to Nguyen et al., each of which is incorporated byreference as if fully set forth herein. Temperature limited heaters aredimensioned to operate with AC frequencies (for example, 60 Hz AC) orwith modulated DC current.

In certain embodiments, ferromagnetic materials are used in temperaturelimited heaters. Ferromagnetic material may self-limit temperature at ornear the Curie temperature of the material and/or the phasetransformation temperature range to provide a reduced amount of heatwhen a time-varying current is applied to the material. In certainembodiments, the ferromagnetic material self-limits temperature of thetemperature limited heater at a selected temperature that isapproximately the Curie temperature and/or in the phase transformationtemperature range. In certain embodiments, the selected temperature iswithin about 35° C., within about 25° C., within about 20° C., or withinabout 10° C. of the Curie temperature and/or the phase transformationtemperature range. In certain embodiments, ferromagnetic materials arecoupled with other materials (for example, highly conductive materials,high strength materials, corrosion resistant materials, or combinationsthereof) to provide various electrical and/or mechanical properties.Some parts of the temperature limited heater may have a lower resistance(caused by different geometries and/or by using different ferromagneticand/or non-ferromagnetic materials) than other parts of the temperaturelimited heater. Having parts of the temperature limited heater withvarious materials and/or dimensions allows for tailoring the desiredheat output from each part of the heater.

Temperature limited heaters may be more reliable than other heaters.Temperature limited heaters may be less apt to break down or fail due tohot spots in the formation. In some embodiments, temperature limitedheaters allow for substantially uniform heating of the formation. Insome embodiments, temperature limited heaters are able to heat theformation more efficiently by operating at a higher average heat outputalong the entire length of the heater. The temperature limited heateroperates at the higher average heat output along the entire length ofthe heater because power to the heater does not have to be reduced tothe entire heater, as is the case with typical constant wattage heaters,if a temperature along any point of the heater exceeds, or is about toexceed, a maximum operating temperature of the heater. Heat output fromportions of a temperature limited heater approaching a Curie temperatureand/or the phase transformation temperature range of the heaterautomatically reduces without controlled adjustment of the time-varyingcurrent applied to the heater. The heat output automatically reduces dueto changes in electrical properties (for example, electrical resistance)of portions of the temperature limited heater. Thus, more power issupplied by the temperature limited heater during a greater portion of aheating process.

In certain embodiments, the system including temperature limited heatersinitially provides a first heat output and then provides a reduced(second heat output) heat output, near, at, or above the Curietemperature and/or the phase transformation temperature range of anelectrically resistive portion of the heater when the temperaturelimited heater is energized by a time-varying current. The first heatoutput is the heat output at temperatures below which the temperaturelimited heater begins to self-limit. In some embodiments, the first heatoutput is the heat output at a temperature about 50° C., about 75° C.,about 100° C., or about 125° C. below the Curie temperature and/or thephase transformation temperature range of the ferromagnetic material inthe temperature limited heater.

The temperature limited heater may be energized by time-varying current(alternating current or modulated direct current) supplied at thewellhead. The wellhead may include a power source and other components(for example, modulation components, transformers, and/or capacitors)used in supplying power to the temperature limited heater. Thetemperature limited heater may be one of many heaters used to heat aportion of the formation.

In certain embodiments, the temperature limited heater includes aconductor that operates as a skin effect or proximity effect heater whentime-varying current is applied to the conductor. The skin effect limitsthe depth of current penetration into the interior of the conductor. Forferromagnetic materials, the skin effect is dominated by the magneticpermeability of the conductor. The relative magnetic permeability offerromagnetic materials is typically between 10 and 1000 (for example,the relative magnetic permeability of ferromagnetic materials istypically at least 10 and may be at least 50, 100, 500, 1000 orgreater). As the temperature of the ferromagnetic material is raisedabove the Curie temperature, or the phase transformation temperaturerange, and/or as the applied electrical current is increased, themagnetic permeability of the ferromagnetic material decreasessubstantially and the skin depth expands rapidly (for example, the skindepth expands as the inverse square root of the magnetic permeability).The reduction in magnetic permeability results in a decrease in the ACor modulated DC resistance of the conductor near, at, or above the Curietemperature, the phase transformation temperature range, and/or as theapplied electrical current is increased. When the temperature limitedheater is powered by a substantially constant current source, portionsof the heater that approach, reach, or are above the Curie temperatureand/or the phase transformation temperature range may have reduced heatdissipation. Sections of the temperature limited heater that are not ator near the Curie temperature and/or the phase transformationtemperature range may be dominated by skin effect heating that allowsthe heater to have high heat dissipation due to a higher resistive load.

An advantage of using the temperature limited heater to heathydrocarbons in the formation is that the conductor is chosen to have aCurie temperature and/or a phase transformation temperature range in adesired range of temperature operation. Operation within the desiredoperating temperature range allows substantial heat injection into theformation while maintaining the temperature of the temperature limitedheater, and other equipment, below design limit temperatures. Designlimit temperatures are temperatures at which properties such ascorrosion, creep, and/or deformation are adversely affected. Thetemperature limiting properties of the temperature limited heaterinhibit overheating or burnout of the heater adjacent to low thermalconductivity “hot spots” in the formation. In some embodiments, thetemperature limited heater is able to lower or control heat outputand/or withstand heat at temperatures above 25° C., 37° C., 100° C.,250° C., 500° C., 700° C., 800° C., 900° C., or higher up to 1131° C.,depending on the materials used in the heater.

The temperature limited heater allows for more heat injection into theformation than constant wattage heaters because the energy input intothe temperature limited heater does not have to be limited toaccommodate low thermal conductivity regions adjacent to the heater. Forexample, in Green River oil shale there is a difference of at least afactor of 3 in the thermal conductivity of the lowest richness oil shalelayers and the highest richness oil shale layers. When heating such aformation, substantially more heat is transferred to the formation withthe temperature limited heater than with the conventional heater that islimited by the temperature at low thermal conductivity layers. The heatoutput along the entire length of the conventional heater needs toaccommodate the low thermal conductivity layers so that the heater doesnot overheat at the low thermal conductivity layers and burn out. Theheat output adjacent to the low thermal conductivity layers that are athigh temperature will reduce for the temperature limited heater, but theremaining portions of the temperature limited heater that are not athigh temperature will still provide high heat output. Because heatersfor heating hydrocarbon formations typically have long lengths (forexample, at least 10 m, 100 m, 300 m, 500 m, 1 km or more up to about 10km), the majority of the length of the temperature limited heater may beoperating below the Curie temperature and/or the phase transformationtemperature range while only a few portions are at or near the Curietemperature and/or the phase transformation temperature range of thetemperature limited heater.

The use of temperature limited heaters allows for efficient transfer ofheat to the formation. Efficient transfer of heat allows for reductionin time needed to heat the formation to a desired temperature. Forexample, in Green River oil shale, pyrolysis typically requires 9.5years to 10 years of heating when using a 12 m heater well spacing withconventional constant wattage heaters. For the same heater spacing,temperature limited heaters may allow a larger average heat output whilemaintaining heater equipment temperatures below equipment design limittemperatures. Pyrolysis in the formation may occur at an earlier timewith the larger average heat output provided by temperature limitedheaters than the lower average heat output provided by constant wattageheaters. For example, in Green River oil shale, pyrolysis may occur in 5years using temperature limited heaters with a 12 m heater well spacing.Temperature limited heaters counteract hot spots due to inaccurate wellspacing or drilling where heater wells come too close together. Incertain embodiments, temperature limited heaters allow for increasedpower output over time for heater wells that have been spaced too farapart, or limit power output for heater wells that are spaced too closetogether. Temperature limited heaters also supply more power in regionsadjacent the overburden and underburden to compensate for temperaturelosses in these regions.

Temperature limited heaters may be advantageously used in many types offormations. For example, in tar sands formations or relatively permeableformations containing heavy hydrocarbons, temperature limited heatersmay be used to provide a controllable low temperature output forreducing the viscosity of fluids, mobilizing fluids, and/or enhancingthe radial flow of fluids at or near the wellbore or in the formation.Temperature limited heaters may be used to inhibit excess coke formationdue to overheating of the near wellbore region of the formation.

In some embodiments, the use of temperature limited heaters eliminatesor reduces the need for expensive temperature control circuitry. Forexample, the use of temperature limited heaters eliminates or reducesthe need to perform temperature logging and/or the need to use fixedthermocouples on the heaters to monitor potential overheating at hotspots.

The temperature limited heaters may be used in conductor-in-conduitheaters. In some embodiments of conductor-in-conduit heaters, themajority of the resistive heat is generated in the conductor, and theheat radiatively, conductively and/or convectively transfers to theconduit. In some embodiments of conductor-in-conduit heaters, themajority of the resistive heat is generated in the conduit.

In some embodiments, a relatively thin conductive layer is used toprovide the majority of the electrically resistive heat output of thetemperature limited heater at temperatures up to a temperature at ornear the Curie temperature and/or the phase transformation temperaturerange of the ferromagnetic conductor. Such a temperature limited heatermay be used as the heating member in an insulated conductor heater. Theheating member of the insulated conductor heater may be located inside asheath with an insulation layer between the sheath and the heatingmember.

Mineral insulated (MI) cables (insulated conductors) for use insubsurface applications, such as heating hydrocarbon containingformations in some applications, are longer, may have larger outsidediameters, and may operate at higher voltages and temperatures than whatis typical in the MI cable industry. For these subsurface applications,the joining of multiple MI cables is needed to make MI cables withsufficient length to reach the depths and distances needed to heat thesubsurface efficiently and to join segments with different functions,such as lead-in cables joined to heater sections. Such long heaters alsorequire higher voltages to provide enough power to the farthest ends ofthe heaters.

Conventional MI cable splice designs are typically not suitable forvoltages above 1000 volts, above 1500 volts, or above 2000 volts and maynot operate for extended periods without failure at elevatedtemperatures, such as over 650° C. (about 1200° F.), over 700° C. (about1290° F.), or over 800° C. (about 1470° F.). Such high voltage, hightemperature applications typically require the compaction of the mineralinsulant in the splice to be as close as possible to or above the levelof compaction in the insulated conductor (MI cable) itself.

The relatively large outside diameter and long length of MI cables forsome applications requires that the cables be spliced while orientedhorizontally. There are splices for other applications of MI cables thathave been fabricated horizontally. These techniques typically use asmall hole through which the mineral insulation (such as magnesium oxidepowder) is filled into the splice and compacted slightly throughvibration and tamping. Such methods do not provide sufficient compactionof the mineral insulation or even, in some cases, allow any compactionof the mineral insulation, and, thus may not be suitable for makingsplices for use at the high voltages needed for these subsurfaceapplications.

Thus, there is a need for splices of insulated conductors that aresimple yet can operate at the high voltages and temperatures in thesubsurface environment over long durations without failure. In addition,the splices may need higher bending and tensile strengths to inhibitfailure of the splice under the weight loads and temperatures that thecables can be subjected to in the subsurface. Techniques and methodsalso may be utilized to reduce electric field intensities in the splicesto reduce leakage currents in the splices and to increase the marginbetween the operating voltage and electrical breakdown. Reducingelectric field intensities may help increase voltage and temperatureoperating ranges of the splices.

FIG. 5 depicts a side view cross-sectional representation of oneembodiment of a fitting for joining insulated conductors. Fitting 250 isa splice or coupling joint for joining insulated conductors 212A, 212B.In certain embodiments, fitting 250 includes sleeve 252 and housings254A, 254B. Housings 254A, 254B may be splice housings, coupling jointhousings, or coupler housings. Sleeve 252 and housings 254A, 254B may bemade of mechanically strong, electrically conductive materials such as,but not limited to, stainless steel. Sleeve 252 and housings 254A, 254Bmay be cylindrically shaped or polygon shaped. Sleeve 252 and housings254A, 254B may have rounded edges, tapered diameter changes, otherfeatures, or combinations thereof, which reduce electric fieldintensities in fitting 250.

Fitting 250 may be used to couple (splice) insulated conductor 212A toinsulated conductor 212B while maintaining the mechanical and electricalintegrity of the jackets (sheaths), insulation, and cores (conductors)of the insulated conductors. Fitting 250 may be used to couple heatproducing insulated conductors with non-heat producing insulatedconductors, to couple heat producing insulated conductors with otherheat producing insulated conductors, or to couple non-heat producinginsulated conductors with other non-heat producing insulated conductors.In some embodiments, more than one fitting 250 is used to couplemultiple heat producing and non-heat producing insulated conductors toprovide a long insulated conductor.

Fitting 250 may be used to couple insulated conductors with differentdiameters, as shown in FIG. 5. For example, the insulated conductors mayhave different core (conductor) diameters, different jacket (sheath)diameters, or combinations of different diameters. Fitting 250 may alsobe used to couple insulated conductors with different metallurgies,different types of insulation, or combinations thereof.

As shown in FIG. 5, housing 254A is coupled to jacket (sheath) 218A ofinsulated conductor 212A and housing 254B is coupled to jacket 218B ofinsulated conductor 212B. In certain embodiments, housings 254A, 254Bare welded, brazed, or otherwise permanently affixed to insulatedconductors 212A, 212B. In some embodiments, housings 254A, 254B aretemporarily or semi-permanently affixed to jackets 218A, 218B ofinsulated conductors 212A, 212B (for example, coupled using threads oradhesives). Fitting 250 may be centered between the end portions of theinsulated conductors 212A, 212B.

In certain embodiments, the interior volumes of sleeve 252 and housings254A, 254B are substantially filled with electrically insulatingmaterial 256. In certain embodiments, “substantially filled” refers toentirely or almost entirely filling the volume or volumes withelectrically insulating material with substantially no macroscopic voidsin the volume or volumes. For example, substantially filled may refer tofilling almost the entire volume with electrically insulating materialthat has some porosity because of microscopic voids (for example, up toabout 40% porosity). Electrically insulating material 256 may includemagnesium oxide, talc, ceramic powders (for example, boron nitride), amixture of magnesium oxide and another electrical insulator (forexample, up to about 50% by weight boron nitride), ceramic cement,mixtures of ceramic powders with certain non-ceramic materials (such astungsten sulfide (WS₂)), or mixtures thereof. For example, magnesiumoxide may be mixed with boron nitride or another electrical insulator toimprove the ability of the electrically insulating material to flow, toimprove the dielectric characteristics of the electrically insulatingmaterial, or to improve the flexibility of the fitting. In someembodiments, electrically insulating material 256 is material similar toelectrical insulation used inside of at least one of insulatedconductors 212A, 212B. Electrically insulating material 256 may havesubstantially similar dielectric characteristics to electricalinsulation used inside of at least one of insulated conductors 212A,212B.

In certain embodiments, first sleeve 252 and housings 254A, 254B aremade up (for example, put together or manufactured) buried or submergedin electrically insulating material 256. Making up sleeve 252 andhousings 254A, 254B buried in electrically insulating material 256inhibits open space from forming in the interior volumes of theportions. Sleeve 252 and housings 254A, 254B have open ends to allowinsulated conductors 212A, 212B to pass through. These open ends may besized to have diameters slightly larger than the outside diameter of thejackets of the insulated conductors.

In certain embodiments, cores 214A, 214B of insulated conductors 212A,212B are joined together at coupling 258. The jackets and insulation ofinsulated conductors 212A, 212B may be cut back or stripped to exposedesired lengths of cores 214A, 214B before joining the cores. Coupling258 may be located in electrically insulating material 256 inside sleeve252.

Coupling 258 may join cores 214A, 214B together, for example, bycompression, crimping, brazing, welding, or other techniques known inthe art. In some embodiments, core 214A is made of different materialthan core 214B. For example, core 214A may be copper while core 214B isstainless steel, carbon steel, or Alloy 180. In such embodiments,special methods may have to be used to weld the cores together. Forexample, the tensile strength properties and/or yield strengthproperties of the cores may have to be matched closely such that thecoupling between the cores does not degrade over time or with use.

In some embodiments, a copper core may be work-hardened before joiningthe core to carbon steel or Alloy 180. In some embodiments, the coresare coupled by in-line welding using filler material (for example,filler metal) between the cores of different materials. For example,Monel® (Special Metals Corporation, New Hartford, N.Y., U.S.A.) nickelalloys may be used as filler material. In some embodiments, copper coresare buttered (melted and mixed) with the filler material before thewelding process.

In an embodiment, insulated conductors 212A, 212B are coupled usingfitting 250 by first sliding housing 254A over jacket 218A of insulatedconductor 212A and, second, sliding housing 254B over jacket 218B ofinsulated conductor 212B. The housings are slid over the jackets withthe large diameter ends of the housings facing the ends of the insulatedconductors. Sleeve 252 may be slid over insulated conductor 212B suchthat it is adjacent to housing 254B. Cores 214A, 214B are joined atcoupling 258 to create a robust electrical and mechanical connectionbetween the cores. The small diameter end of housing 254A is joined (forexample, welded) to jacket 218A of insulated conductor 212A. Sleeve 252and housing 254B are brought (moved or pushed) together with housing254A to form fitting 250. The interior volume of fitting 250 may besubstantially filled with electrically insulating material while thesleeve and the housings are brought together. The interior volume of thecombined sleeve and housings is reduced such that the electricallyinsulating material substantially filling the entire interior volume iscompacted. Sleeve 252 is joined to housing 254B and housing 254B isjoined to jacket 218B of insulated conductor 212B. The volume of sleeve252 may be further reduced, if additional compaction is desired.

In certain embodiments, the interior volumes of housings 254A, 254Bfilled with electrically insulating material 256 have tapered shapes.The diameter of the interior volumes of housings 254A, 254B may taperfrom a smaller diameter at or near the ends of the housings coupled toinsulated conductors 212A, 212B to a larger diameter at or near the endsof the housings located inside sleeve 252 (the ends of the housingsfacing each other or the ends of the housings facing the ends of theinsulated conductors). The tapered shapes of the interior volumes mayreduce electric field intensities in fitting 250. Reducing electricfield intensities in fitting 250 may reduce leakage currents in thefitting at increased operating voltages and temperatures, and mayincrease the margin to electrical breakdown. Thus, reducing electricfield intensities in fitting 250 may increase the range of operatingvoltages and temperatures for the fitting.

In some embodiments, the insulation from insulated conductors 212A, 212Btapers from jackets 218A, 218B down to cores 214A, 214B in the directiontoward the center of fitting 250 in the event that the electricallyinsulating material 256 is a weaker dielectric than the insulation inthe insulated conductors. In some embodiments, the insulation frominsulated conductors 212A, 212B tapers from jackets 218A, 218B down tocores 214A, 214B in the direction toward the insulated conductors in theevent that electrically insulating material 256 is a stronger dielectricthan the insulation in the insulated conductors. Tapering the insulationfrom the insulated conductors reduces the intensity of electric fieldsat the interfaces between the insulation in the insulated conductors andthe electrically insulating material within the fitting.

FIG. 6 depicts a tool that may be used to cut away part of the inside ofinsulated conductors 212A, 212B (for example, electrical insulationinside the jacket of the insulated conductor). Cutting tool 260 mayinclude cutting teeth 262 and drive tube 264. Drive tube 264 may becoupled to the body of cutting tool 260 using, for example, a weld or abraze. In some embodiments, no cutting tool is needed to cut awayelectrical insulation from inside the jacket.

Sleeve 252 and housings 254A, 254B may be coupled together using anymeans known in the art such as brazing, welding, or crimping. In someembodiments, as shown in FIG. 7, sleeve 252 and housings 254A, 254B havethreads that engage to couple the pieces together.

As shown in FIGS. 5 and 7, in certain embodiments, electricallyinsulating material 256 is compacted during the assembly process. Theforce to press the housings 254A, 254B toward each other may put apressure on electrically insulating material 256 of, for example, atleast 25,000 pounds per square inch up to 55,000 pounds per square inchin order to provide acceptable compaction of the insulating material.The tapered shapes of the interior volumes of housings 254A, 254B andthe make-up of electrically insulating material 256 may enhancecompaction of the electrically insulating material during the assemblyprocess to the point where the dielectric characteristics of theelectrically insulating material are, to the extent practical,comparable to that within insulated conductors 212A, 212B. Methods anddevices to facilitate compaction include, but are not limited to,mechanical methods (such as shown in FIG. 10), pneumatic, hydraulic(such as shown in FIGS. 11 and 12), swaged, or combinations thereof.

The combination of moving the pieces together with force and thehousings having the tapered interior volumes compacts electricallyinsulating material 256 using both axial and radial compression. Bothaxial and radial compressing electrically insulating material 256provides more uniform compaction of the electrically insulatingmaterial. In some embodiments, vibration and/or tamping of electricallyinsulating material 256 may also be used to consolidate the electricallyinsulating material. Vibration (and/or tamping) may be applied either atthe same time as application of force to push the housings 254A, 254Btogether, or vibration (and/or tamping) may be alternated withapplication of such force. Vibration and/or tamping may reduce bridgingof particles in electrically insulating material 256.

In the embodiment depicted in FIG. 7, electrically insulating material256 inside housings 254A, 254B is compressed mechanically by tighteningnuts 266 against ferrules 268 coupled to jackets 218A, 218B. Themechanical method compacts the interior volumes of housings 254A, 254Bbecause of the tapered shape of the interior volumes. Ferrules 268 maybe copper or other soft metal ferrules. Nuts 266 may be stainless steelor other hard metal nut that is movable on jackets 218A, 218B. Nuts 266may engage threads on housings 254A, 254B to couple to the housings. Asnuts 266 are threaded onto housings 254A, 254B, nuts 266 and ferrules268 work to compress the interior volumes of the housings. In someembodiments, nuts 266 and ferrules 268 may work to move housings 254A,254B further onto sleeve 252 (using the threaded coupling between thepieces) and compact the interior volume of the sleeve. In someembodiments, housings 254A, 254B and sleeve 252 are coupled togetherusing the threaded coupling before the nut and ferrule are swaged downon the second portion. As the interior volumes inside housings 254A,254B are compressed, the interior volume inside sleeve 252 may also becompressed. In some embodiments, nuts 266 and ferrules 268 may act tocouple housings 254A, 254B to insulated conductors 212A, 212B.

In certain embodiments, multiple insulated conductors are splicedtogether in an end fitting. For example, three insulated conductors maybe spliced together in an end fitting to couple electrically theinsulated conductors in a 3-phase wye configuration. FIG. 8A depicts aside view of a cross-sectional representation of an embodiment ofthreaded fitting 270 for coupling three insulated conductors 212A, 212B,212C. FIG. 8B depicts a side view of a cross-sectional representation ofan embodiment of welded fitting 270 for coupling three insulatedconductors 212A, 212B, 212C. As shown in FIGS. 8A and 8B, insulatedconductors 212A, 212B, 212C may be coupled to fitting 270 through endcap 272. End cap 272 may include three strain relief fittings 274through which insulated conductors 212A, 212B, 212C pass.

Cores 214A, 214B, 214C of the insulated conductors may be coupledtogether at coupling 258. Coupling 258 may be, for example, a braze(such as a silver braze or copper braze), a welded joint, or a crimpedjoint. Coupling cores 214A, 214B, 214C at coupling 258 electrically jointhe three insulated conductors for use in a 3-phase wye configuration.

As shown in FIG. 8A, end cap 272 may be coupled to main body 276 offitting 270 using threads. Threading of end cap 272 and main body 276may allow the end cap to compact electrically insulating material 256inside the main body. At the end of main body 276 opposite of end cap272 is cover 278. Cover 278 may also be attached to main body 276 bythreads. In certain embodiments, compaction of electrically insulatingmaterial 256 in fitting 270 is enhanced through tightening of cover 278into main body 276, by crimping of the main body after attachment of thecover, or a combination of these methods.

As shown in FIG. 8B, end cap 272 may be coupled to main body 276 offitting 270 using welding, brazing, or crimping. End cap 272 may bepushed or pressed into main body 276 to compact electrically insulatingmaterial 256 inside the main body. Cover 278 may also be attached tomain body 276 by welding, brazing, or crimping. Cover 278 may be pushedor pressed into main body 276 to compact electrically insulatingmaterial 256 inside the main body. Crimping of the main body afterattachment of the cover may further enhance compaction of electricallyinsulating material 256 in fitting 270.

In some embodiments, as shown in FIGS. 8A and 8B, plugs 280 closeopenings or holes in cover 278. For example, the plugs may be threaded,welded, or brazed into openings in cover 278. The openings in cover 278may allow electrically insulating material 256 to be provided insidefitting 270 when cover 278 and end cap 272 are coupled to main body 276.The openings in cover 278 may be plugged or covered after electricallyinsulating material 256 is provided inside fitting 270. In someembodiments, openings are located on main body 276 of fitting 270.Openings on main body 276 may be plugged with plugs 280 or other plugs.

In some embodiments, cover 278 includes one or more pins. In someembodiments, the pins are or are part of plugs 280. The pins may engagea torque tool that turns cover 278 and tightens the cover on main body276. An example of torque tool 282 that may engage the pins is depictedin FIG. 9. Torque tool 282 may have an inside diameter thatsubstantially matches the outside diameter of cover 278 (depicted inFIG. 8A). As shown in FIG. 9, torque tool 282 may have slots or otherdepressions that are shaped to engage the pins on cover 278. Torque tool282 may include recess 284. Recess 284 may be a square drive recess orother shaped recess that allows operation (turning) of the torque tool.

FIG. 10 depicts an embodiment of clamp assemblies 286A,B that may beused to mechanically compact fitting 250. Clamp assemblies 286A,B may beshaped to secure fitting 250 in place at the shoulders of housings 254A,254B. Threaded rods 288 may pass through holes 290 of clamp assemblies286A,B. Nuts 292, along with washers, on each of threaded rods 288 maybe used to apply force on the outside faces of each clamp assembly andbring the clamp assemblies together such that compressive forces areapplied to housings 254A, 254B of fitting 250. These compressive forcescompact electrically insulating material inside fitting 250.

In some embodiments, clamp assemblies 286 are used in hydraulic,pneumatic, or other compaction methods. FIG. 11 depicts an exploded viewof an embodiment of hydraulic compaction machine 294. FIG. 12 depicts arepresentation of an embodiment of assembled hydraulic compactionmachine 294. As shown in FIGS. 11 and 12, clamp assemblies 286 may beused to secure fitting 250 (depicted, for example, in FIG. 5) in placewith insulated conductors coupled to the fitting. At least one clampassembly (for example, clamp assembly 286A) may be moveable together tocompact the fitting in the axial direction. Power unit 296, shown inFIG. 11, may be used to power compaction machine 294.

FIG. 13 depicts an embodiment of fitting 250 and insulated conductors212A, 212B secured in clamp assembly 286A and clamp assembly 286B beforecompaction of the fitting and insulated conductors. As shown in FIG. 13,the cores of insulated conductors 212A, 212B are coupled using coupling258 at or near the center of sleeve 252. Sleeve 252 is slid over housing254A, which is coupled to insulated conductor 212A. Sleeve 252 andhousing 254A are secured in fixed (non-moving) clamp assembly 286B.Insulated conductor 212B passes through housing 254B and movable clampassembly 286A. Insulated conductor 212B may be secured by another clampassembly fixed relative to clamp assembly 286B (not shown). Clampassembly 286A may be moved towards clamp assembly 286B to couple housing254B to sleeve 252 and compact electrically insulating material insidethe housings and the sleeve. Interfaces between insulated conductor 212Aand housing 254A, between housing 254A and sleeve 252, between sleeve252 and housing 254B, and between housing 254B and insulated conductor212B may then be coupled by welding, brazing, or other techniques knownin the art.

FIG. 14 depicts a side view representation of an embodiment of fitting298 for joining insulated conductors. Fitting 298 may be a cylinder orsleeve that has sufficient clearance between the inside diameter of thesleeve and the outside diameters of insulated conductors 212A, 212B suchthat the sleeve fits over the ends of the insulated conductors. Thecores of insulated conductors 212A, 212B may be joined inside fitting298. The jackets and insulation of insulated conductors 212A, 212B maybe cut back or stripped to expose desired lengths of the cores beforejoining the cores. Fitting 298 may be centered between the end portionsof insulated conductors 212A, 212B.

Fitting 298 may be used to couple insulated conductor 212A to insulatedconductor 212B while maintaining the mechanical and electrical integrityof the jackets, insulation, and cores of the insulated conductors.Fitting 298 may be used to couple heat producing insulated conductorswith non-heat producing insulated conductors, to couple heat producinginsulated conductors with other heat producing insulated conductors, orto couple non-heat producing insulated conductors with other non-heatproducing insulated conductors. In some embodiments, more than onefitting 298 is used in to couple multiple heat producing and non-heatproducing insulated conductors to produce a long insulated conductor.

Fitting 298 may be used to couple insulated conductors with differentdiameters. For example, the insulated conductors may have different corediameters, different jacket diameters, or combinations of differentdiameters. Fitting 298 may also be used to couple insulated conductorswith different metallurgies, different types of insulation, or acombination thereof.

In certain embodiments, fitting 298 has at least one angled end. Forexample, the ends of fitting 298 may be angled relative to thelongitudinal axis of the fitting. The angle may be, for example, about45° or between 30° and 60°. Thus, the ends of fitting 298 may havesubstantially elliptical cross-sections. The substantially ellipticalcross-sections of the ends of fitting 298 provide a larger area forwelding or brazing of the fitting to insulated conductors 212A, 212B.The larger coupling area increases the strength of spliced insulatedconductors. In the embodiment shown in FIG. 14, the angled ends offitting 298 give the fitting a substantially parallelogram shape.

The angled ends of fitting 298 provide higher tensile strength andhigher bending strength for the fitting than if the fitting had straightends by distributing loads along the fitting. Fitting 298 may beoriented so that when insulated conductors 212A, 212B and the fittingare spooled (for example, on a coiled tubing installation), the angledends act as a transition in stiffness from the fitting body to theinsulated conductors. This transition reduces the likelihood of theinsulated conductors to kink or crimp at the end of the fitting body.

As shown in FIG. 14, fitting 298 includes opening 300. Opening 300allows electrically insulating material (such as electrically insulatingmaterial 256, depicted in FIG. 5) to be provided (filled) inside fitting298. Opening 300 may be a slot or other longitudinal opening extendingalong part of the length of fitting 298. In certain embodiments, opening300 extends substantially the entire gap between the ends of insulatedconductors 212A, 212B inside fitting 298. Opening 300 allowssubstantially the entire volume (area) between insulated conductors212A, 212B, and around any welded or spliced joints between theinsulated conductors, to be filled with electrically insulating materialwithout the insulating material having to be moved axially toward theends of the volume between the insulated conductors. The width ofopening 300 allows electrically insulating material to be forced intothe opening and packed more tightly inside fitting 298, thus, reducingthe amount of void space inside the fitting. Electrically insulatingmaterial may be forced through the slot into the volume betweeninsulated conductors 212A, 212B, for example, with a tool with thedimensions of the slot. The tool may be forced into the slot to compactthe insulating material. Then, additional insulating material may beadded and the compaction is repeated. In some embodiments, theelectrically insulating material may be further compacted inside fitting298 using vibration, tamping, or other techniques. Further compactingthe electrically insulating material may more uniformly distribute theelectrically insulating material inside fitting 298.

After filling electrically insulating material inside fitting 298 and,in some embodiment, compaction of the electrically insulating material,opening 300 may be closed. For example, an insert or other covering maybe placed over the opening and secured in place. FIG. 15 depicts a sideview representation of an embodiment of fitting 298 with opening 300covered with insert 302. Insert 302 may be welded or brazed to fitting298 to close opening 300. In some embodiments, insert 302 is ground orpolished so that the insert if flush on the surface of fitting 298. Alsodepicted in FIG. 15, welds or brazes 304 may be used to secure fitting298 to insulated conductors 212A, 212B.

After opening 300 is closed, fitting 298 may be compacted mechanically,hydraulically, pneumatically, or using swaging methods to compactfurther the electrically insulating material inside the fitting. Furthercompaction of the electrically insulating material reduces void volumeinside fitting 298 and reduces the leakage currents through the fittingand increases the operating range of the fitting (for example, themaximum operating voltages or temperatures of the fitting).

In certain embodiments, fitting 298 includes certain features that mayfurther reduce electric field intensities inside the fitting. Forexample, fitting 298 or coupling 258 of the cores of the insulatedconductors inside the fitting may include tapered edges, rounded edges,or other smoothed out features to reduce electric field intensities.FIG. 16 depicts an embodiment of fitting 298 with electric fieldreducing features at coupling 258 between insulated conductors 212A,212B. As shown in FIG. 16, coupling 258 is a welded joint with asmoothed out or rounded profile to reduce electric field intensityinside fitting 298. In addition, fitting 298 has a tapered interiorvolume to increase the volume of electrically insulating material insidethe fitting. Having the tapered and larger volume may reduce electricfield intensities inside fitting 298.

In some embodiments, electric field stress reducers may be locatedinside fitting 298 to decrease the electric field intensity. FIG. 17depicts an embodiment of electric field stress reducer 306. Reducer 306may be located in the interior volume of fitting 298 (shown in FIG. 16).Reducer 306 may be a split ring or other separable piece so that thereducer can be fitted around cores 214A, 214B of insulated conductors212A, 212B after they are joined (shown in FIG. 16).

FIGS. 18 and 19 depict cross-sectional representations of anotherembodiment of fitting 250 used for joining insulated conductors. FIG. 18depicts a cross-sectional representation of fitting 250 as insulatedconductors 212A, 212B are being moved into the fitting. FIG. 19 depictsa cross-sectional representation of fitting 250 with insulatedconductors 212A, 212B joined inside the fitting. In certain embodiments,fitting 250 includes sleeve 252 and coupling 258.

Fitting 250 may be used to couple (splice) insulated conductor 212A toinsulated conductor 212B while maintaining the mechanical and electricalintegrity of the jackets (sheaths), insulation, and cores (conductors)of the insulated conductors. Fitting 250 may be used to couple heatproducing insulated conductors with non-heat producing insulatedconductors, to couple heat producing insulated conductors with otherheat producing insulated conductors, or to couple non-heat producinginsulated conductors with other non-heat producing insulated conductors.In some embodiments, more than one fitting 250 is used to couplemultiple heat producing and non-heat producing insulated conductors toprovide a long insulated conductor.

Fitting 250 may be used to couple insulated conductors with differentdiameters. For example, the insulated conductors may have different core(conductor) diameters, different jacket (sheath) diameters, orcombinations of different diameters. Fitting 250 may also be used tocouple insulated conductors with different metallurgies, different typesof insulation, or combinations thereof.

Coupling 258 is used to join and electrically couple cores 214A, 214B ofinsulated conductors 212A, 212B inside fitting 250. Coupling 258 may bemade of copper or another suitable electrical conductor. In certainembodiments, cores 214A, 214B are press fit or pushed into coupling 258.In some embodiments, coupling 258 is heated to enable cores 214A, 214Bto be slid into the coupling. In some embodiments, core 214A is made ofdifferent material than core 214B. For example, core 214A may be copperwhile core 214B is stainless steel, carbon steel, or Alloy 180. In suchembodiments, special methods may have to be used to weld the corestogether. For example, the tensile strength properties and/or yieldstrength properties of the cores may have to be matched closely suchthat the coupling between the cores does not degrade over time or withuse.

In some embodiments, coupling 258 includes one or more grooves on theinside of the coupling. The grooves may inhibit particles from enteringor exiting the coupling after the cores are joined in the coupling. Insome embodiments, coupling 258 has a tapered inner diameter (forexample, tighter inside diameter towards the center of the coupling).The tapered inner diameter may provide a better press fit betweencoupling 258 and cores 214A, 214B.

In certain embodiments, electrically insulating material 256 is locatedinside sleeve 252. In some embodiments, electrically insulating material256 is magnesium oxide or a mixture of magnesium oxide and boron nitride(80% magnesium oxide and 20% boron nitride by weight). Electricallyinsulating material 256 may include magnesium oxide, talc, ceramicpowders (for example, boron nitride), a mixture of magnesium oxide andanother electrical insulator (for example, up to about 50% by weightboron nitride), ceramic cement, mixtures of ceramic powders with certainnon-ceramic materials (such as tungsten sulfide (WS₂)), or mixturesthereof. For example, magnesium oxide may be mixed with boron nitride oranother electrical insulator to improve the ability of the electricallyinsulating material to flow, to improve the dielectric characteristicsof the electrically insulating material, or to improve the flexibilityof the fitting. In some embodiments, electrically insulating material256 is material similar to electrical insulation used inside of at leastone of insulated conductors 212A, 212B. Electrically insulating material256 may have substantially similar dielectric characteristics toelectrical insulation used inside of at least one of insulatedconductors 212A, 212B.

In certain embodiments, the interior volumes of sleeve 252 issubstantially filled with electrically insulating material 256. Incertain embodiments, “substantially filled” refers to entirely or almostentirely filling the volume or volumes with electrically insulatingmaterial with substantially no macroscopic voids in the volume orvolumes. For example, substantially filled may refer to filling almostthe entire volume with electrically insulating material that has someporosity because of microscopic voids (for example, up to about 40%porosity).

In some embodiments, sleeve 252 has one or more grooves 308. Grooves 308may inhibit electrically insulating material 256 from moving out ofsleeve 252 (for example, the grooves trap the electrically insulatingmaterial in the sleeve).

In certain embodiments, electrically insulating material 256 has concaveshaped end portions at or near the edges of coupling 258, as shown inFIG. 18. The concave shapes of electrically insulating material 256 mayenhance coupling with electrical insulators 216A, 216B of insulatedconductors 212A, 212B. In some embodiments, electrical insulators 216A,216B have convex shaped (or tapered) end portions to enhance couplingwith electrically insulating material 256. The end portions ofelectrically insulating material 256 and electrical insulators 216A,216B may comingle or mix under the pressure applied during joining ofthe insulated conductors. The comingling or mixing of the insulationmaterials may enhance the coupling between the insulated conductors.

In certain embodiments, insulated conductors 212A, 212B are joined withfitting 250 by moving (pushing) the insulated conductors togethertowards the center of the fitting. Cores 214A, 214B are brought togetherinside coupling 258 with the movement of insulated conductors 212A,212B. After insulated conductors 212A, 212B are moved together intofitting 250, the fitting and end portions of the insulated conductorsinside the fitting may be compacted or pressed to secure the insulatedconductors in the fitting and compress electrically insulating material256. Clamp assemblies or other similar devices may be used to bringtogether insulated conductors 212A, 212B and fitting 250. In certainembodiments, the force to compress electrically insulating material 256is, for example, at least 25,000 pounds per square inch up to 55,000pounds per square inch in order to provide acceptable compaction of theinsulating material. The compaction of electrically insulating material256 during the assembly process may provide dielectric characteristicsfor the electrically insulating material that are, to the extentpractical, comparable to that within insulated conductors 212A, 212B.Methods and devices to facilitate compaction include, but are notlimited to, mechanical methods, pneumatic, hydraulic, swaged, orcombinations thereof.

In some embodiments, end portions of sleeve 252 are coupled (welded orbrazed) to jackets 218A, 218B of insulated conductors 212A, 212B. Insome embodiments, a support sleeve and/or strain reliefs are placed overfitting 250 to provide additional strength to the fitting.

FIGS. 20 and 21 depict cross-sectional representations of yet anotherembodiment of fitting 250 used for joining insulated conductors. FIG. 20depicts a cross-sectional representation of fitting 250 as insulatedconductors 212A, 212B are being moved into the fitting. FIG. 21 depictsa cross-sectional representation of fitting 250 with insulatedconductors 212A, 212B joined inside the fitting in a final position. Theembodiment of fitting 250 depicted in FIGS. 20 and 21 may be similar tothe embodiment of fitting 250 depicted in FIGS. 18 and 19.

In certain embodiments, fitting 250, as shown in FIGS. 20 and 21,includes sleeve 252 and coupling 258. Coupling 258 is used to join andelectrically couple cores 214A, 214B of insulated conductors 212A, 212Binside fitting 250. Coupling 258 may be made of copper or anothersuitable soft metal conductor. In some embodiments, coupling 258 is usedto couple cores of different diameters. Thus, coupling 258 may havehalves with different inside diameters to match the diameters of thecores.

In certain embodiments, cores 214A, 214B are press fit or pushed intocoupling 258 as insulated conductors 212A, 212B are pushed into sleeve252. In some embodiments, coupling 258 has a tapered inner diameter (forexample, tighter inside diameter towards the center of the coupling), asshown in FIG. 20. The tapered inner diameter may provide a better pressfit between coupling 258 and cores 214A, 214B and increase the interfacelength between the cores and the coupling. Increasing the interfacelength between coupling 258 and cores 214A, 214B decreases resistancebetween the cores and the coupling and inhibits arcing when electricalpower is applied to insulated conductors 212A, 212B.

In certain embodiments, cores 214A, 214B are pushed together to thefinal position depicted in FIG. 21 with clearance 309 between the endsof the cores. Clearance 309 is a gap or space between the ends of cores214A, 214B. In some embodiments, clearance 309 is between about 1 miland about 15 mils or between about 2 mils and about 5 mils.

With clearance 309 between the ends of cores 214A, 214B, movement ofinsulated conductors 212A, 212B as the insulated conductors are pushedinto sleeve 252 is limited by compression of electrical insulators 216A,216B against electrically insulating material 256 and not the interfacebetween the ends of the cores. Thus, maintaining clearance 309 betweenthe ends of cores 214A, 214B provides better (more) compression ofelectrically insulating material 256 and electrical insulators 216A,216B inside sleeve 252 in the final position depicted in FIG. 21. Bettercompression of electrically insulating material 256 and electricalinsulators 216A, 216B provides a more reliable fitting 250 with betterelectrical characteristics.

Additionally, maintaining clearance 309 between the ends of cores 214A,214B inhibits the cores from being pushed against each other and causingbuckling or other deformation of the cores. Pushing cores 214A, 214Btogether inside coupling 258 allows for the cores to be coupled withoutwelding, heating, or otherwise raising the temperature of the cores.Keeping the temperature of cores 214A, 214B reduced during joining ofthe cores keeps the core material (copper) from softening or flowing.Maintaining the hardness of cores 214A, 214B may provide betterelectrical performance of fitting 250.

In certain embodiments, electrically insulating material 256 has concaveshaped end portions at or near the edges of coupling 258, as depicted inFIG. 20. The concave shaped end portions may have angled edges to form afemale type angle shape, as depicted in FIG. 20. The concave shaped endportions of electrically insulating material 256 may enhance couplingwith electrical insulators 216A, 216B of insulated conductors 212A,212B. In some embodiments, electrical insulators 216A, 216B have convexshaped (or male angled edges) end portions to enhance coupling withelectrically insulating material 256. Compressing the shaped endportions against each other may spread out the edges of the end portionsand remove discontinuities between the end portions. Having shaped endportions of electrically insulating material 256 and electricalinsulators 216A, 216B improves compression and/or bridging between theelectrically insulating material and electrical insulators under thepressure applied during joining of insulated conductors 212A, 212B.Compression of the insulation materials enhances the electricalinsulation properties of fitting 250.

In certain embodiments, insulated conductors 212A, 212B are moved aselected distance into fitting 250 to provide a desired compression ofinsulation material in the fitting and a desired coupling between cores214A, 214B and coupling 258. In some embodiments, insulated conductors212A, 212B are moved the selected distance with a selected amount offorce to provide the desired compression and desired coupling. Hydraulicpressure may be used to provide the force to push insulated conductors212A, 212B into fitting 250. As an example, insulated conductors 212A,212B may each be moved between about ⅞″ (about 2.2 cm) and about 1″(about 2.5 cm) into fitting 250 with a hydraulic pressure of betweenabout 2800 psi (19,300 kPa) and about 3000 psi (about 20,680 kPa).

FIG. 22 depicts an embodiment of blocks of electrically insulatingmaterial in position around cores of joined insulated conductors. Core214A of insulated conductor 212A is coupled to core 214B of insulatedconductor 212B at coupling 258. Cores 214A, 214B are exposed by removingportions of electrical insulators 216A, 216B and jackets 218A, 218Bsurrounding the cores at the ends of insulated conductors 212A, 212B.

In some embodiments, cores 214A, 214B have different diameters. In suchembodiments, coupling 258 may taper from the diameter of core 214A tothe diameter of core 214B. In some embodiments, cores 214A, 214B includedifferent materials. Coupling 258 may compensate for the differentmaterials in the cores. For example, coupling 258 may include a blend ormixture of materials in the cores.

In certain embodiments, one or more blocks of electrically insulatingmaterial 256 are placed around the exposed portions of cores 214A, 214B,as shown in FIG. 22. Blocks of electrically insulating material 256 maybe made of, for example, magnesium oxide or a mixture of magnesium oxideand another electrical insulator. The blocks of electrically insulatingmaterial 256 may be hard or soft blocks of material depending on thetype of compaction desired. A desired number of blocks of electricallyinsulating material 256 may be placed around the exposed portions ofcores 214A, 214B such that the blocks substantially completely surroundthe exposed core portions. The number of blocks of electricallyinsulating material 256 may vary based on, for example, the lengthand/or diameter of the exposed core portions and/or the size of theblocks of electrically insulating material. In certain embodiments, fourblocks of electrically insulating material 256 are used to surround theexposed portions of the cores.

FIG. 22 depicts two blocks of electrically insulating material 256A,256B surrounding one half (a semi-circle) of the exposed portions ofcores 214A, 214B. The depicted blocks of electrically insulatingmaterial 256 are semi-circular blocks that fit snugly around the outsidediameters of the exposed core portions. In the embodiment depicted inFIG. 22, two additional blocks of electrically insulating material 256would be placed on the exposed core portions to surround the exposedcore portions with electrically insulating material. FIG. 23 depicts anembodiment of four blocks of electrically insulating material 256A,256B, 256C, 256D in position surrounding the cores of joined insulatedconductors 212A, 212B.

In certain embodiments, blocks of electrically insulating material 256have inside diameters sized and/or shaped to match the outside diametersof the exposed portions of cores 214A, 214B. Matching the insidediameters of the blocks with the outside diameters of the exposed coreportions may provide a snug fit between the blocks and the exposed coreportions and inhibit or reduce gap formation during compaction of theblocks.

In some embodiments, one or more blocks of electrically insulatingmaterial 256 have a tapered inside diameter to match a tapered outerdiameter of coupling 258 and/or the exposed portions of cores 214A,214B, as shown in FIG. 22. The inside diameter of the blocks ofelectrically insulating material 256 may be formed by sanding orgrinding the inner diameter of the blocks to the desired tapered shape.

After blocks of electrically insulating material 256 have been placedaround the exposed portions of the cores (as shown in FIG. 23), a sleeveor other cylindrical covering is placed over the joined insulatedconductors to substantially cover the blocks and at least a portion ofeach of the insulated conductors. FIG. 24 depicts an embodiment of innersleeve 252A placed over joined insulated conductors 212A, 212B. Innersleeve 252A may be a material the same as or similar to material usedfor jackets 218A, 218B of insulated conductors 212A, 212B. For example,inner sleeve 252A and jackets 218A, 218B may be 304 stainless steel.Inner sleeve 252A and jackets 218A, 218B are typically made of materialsthat can be welded together.

Inner sleeve 252A has a tight or snug fit over jackets 218A, 218B ofinsulated conductors 212A, 212B. In some embodiments, inner sleeve 252Aincludes axial and/or radial grooves in the outer surface of the sleeve.In certain embodiments, inner sleeve 252A includes alignment ridge 310.Alignment ridge 310 is located at or near a center of the couplingbetween insulated conductors 212A, 212B.

After the inner sleeve has been placed around the blocks of electricallyinsulating material (as shown in FIG. 24), an outer sleeve or othercylindrical covering is placed over the inner sleeve. FIG. 25 depicts anembodiment of outer sleeve 252B placed over inner sleeve 252A and joinedinsulated conductors 212A, 212B. In certain embodiments, outer sleeve252B has a shorter length than inner sleeve 252A. In certainembodiments, outer sleeve 252B has opening 312. Opening 312 may belocated at or near a center of outer sleeve 252B. Opening 312 may bealigned with alignment ridge 310 on inner sleeve 252A (the alignmentridge is viewed through the opening). In some embodiments, outer sleeve252B is made of two or more pieces. For example, the outer sleeve may betwo-pieces put together in a clam-shell configuration. The pieces may bewelded or otherwise coupled to form the outer sleeve. In someembodiments, outer sleeve 252B includes axial and/or radial grooves inthe inner surface of the sleeve.

Outer sleeve 252B may be a material the same as or similar to materialused for inner sleeve 252A and jackets 218A, 218B (for example, 304stainless steel). Outer sleeve 252B may have a tight or snug fit overinner sleeve 252A. After outer sleeve 252B and inner sleeve 252A areplaced over jackets 218A, 218B of insulated conductors 212A, 212B, thesleeves may be permanently coupled (for example, welded) to jackets218A, 218B. Sleeves 252A, 252B may be permanently coupled to jackets218A, 218B such that the ends of the sleeves are substantially sealed(there are no leaks at the ends of the sleeves that allow air or otherfluids to enter or exit the ends of the sleeves). After coupling ofsleeves 252A, 252B to jackets 218A, 218B, opening 312 is the only portfor fluid to enter/exit outer sleeve 252B and there the interior ofinner sleeve 252A is substantially sealed.

In certain embodiments, fluid (for example, hydraulic fluid) is providedinto the interior volume of outer sleeve 252B through opening 312. Incertain embodiments, the fluid is hydraulic oil. In some embodiments,the fluid includes other fluids such as molten salt or gas. In someembodiments, the fluid is heated during pressurization.

The fluid provided into the interior volume of outer sleeve 252B may bepressurized to compact or compress inner sleeve 252A and electricallyinsulating material 256. For example, the fluid may be hydraulicallypressurized using a hand pump or another suitable hydraulic pressurizingpump. Pressurizing the fluid inside outer sleeve 252B may provideisostatic pressure to compress inner sleeve 252A.

Outer sleeve 252B may be hard or non-susceptible to compaction underpressure while inner sleeve 252A is susceptible to compaction underpressure. For example, inner sleeve 252A may be thinner than outersleeve 252B and/or the inner sleeve may be heat treated (annealed) to besofter than the outer sleeve.

The fluid inside outer sleeve 252B is pressurized to a selected pressureor into a selected pressure range to compact inner sleeve 252A andelectrically insulating material 256 to a desired compaction level. Insome embodiments, the fluid inside outer sleeve 252B is pressurized to apressure between about 15,000 psi (about 100,000 kPa) and about 20,000psi (about 140,000 kPa). In some embodiments, the fluid may bepressurized to higher pressures (for example, pressurized up to about35,000 psi (about 240,000 kPa)).

Pressurizing the fluid to such pressures deforms inner sleeve 252A bycompressing the inner sleeve and compacts electrically insulatingmaterial 256 inside the inner sleeve. Inner sleeve 252A may beuniformally deformed by the fluid pressure inside outer sleeve 252B. Incertain embodiments, electrically insulating material 256 is compactedsuch that the electrically insulating material has dielectric propertiessimilar to or better than the dielectric properties of the electricalinsulator in at least one of the joined insulated conductors. Using thepressurized fluid to compress and compact inner sleeve 252A andelectrically insulating material 256 may allow the insulated conductorsto be joined in the sleeves in a horizontal configuration. Joining theinsulated conductors in a horizontal configuration allows longer lengthsof insulated conductors to be joined together without the need forcomplicated or expensive cable hanging systems.

In some embodiments, the ends of insulated conductors may have chamfersor other tapering to allow for compression of the inner sleeve. FIG. 26depicts an embodiment of a chamfered end of an insulated conductor aftercompression. Insulated conductor 212 includes chamfer 314 inside innersleeve 252A. Chamfer 314 may inhibit kinking or buckling of inner sleeve252A during compression.

In some embodiments, electrically insulating material powder is addedinto the interior of inner sleeve 252A before sealing and compaction ofthe inner sleeve. The electrically insulating material powder maypenetrate and fill voids inside the inner sleeve (such as in the recessformed between a chamfer on the insulated conductor and the innersleeve). Use of electrically insulating material powder may also reducethe number of interfaces in compacted electrically insulating material.In some embodiments, electrically insulating material powder is usedinstead of blocks of electrically insulating material.

In some embodiments, an additive such as a dopant or another additionalmaterial may be added to the electrically insulating material. Theadditive may improve the dielectric properties of the electricallyinsulating material. For example, the additive may increase thedielectric strength of the electrically insulating material.

In certain embodiments, mechanical and/or hydraulic compaction is usedto radially compact electrically insulating material (for example,electrically insulating material in powder form) at the coupling ofjoined insulated conductors. FIG. 27 depicts an embodiment of first half316A of compaction device 316 to be used for compaction of electricallyinsulating material at a coupling of insulated conductors. The secondhalf of device 316 has a similar shape and size as first half 316Adepicted in FIG. 27. The first half and second half of device 316 arecoupled together to form the device around a section of insulatedconductors to be joined together.

FIG. 28 depicts an embodiment of device 316 coupled together aroundinsulated conductors 212A, 212B. The jackets and electrical insulatorsurrounding the cores of insulated conductors 212A, 212B have beenremoved to expose the portions of the cores located inside device 316.

As shown in FIG. 27, first half 316A includes first half 318A of opening318 that is formed in the top of device 316 when the two halves of thedevice are coupled together. Opening 318 allows electrically insulatingmaterial and/or other materials to be provided into the space aroundexposed cores of the insulated conductors. In certain embodiments,electrically insulating material powder is provided into device 316.

As shown in FIG. 28, after at least some electrically insulatingmaterial is provided through opening 318 into device 316 around theexposed cores, first plunger 320A is inserted into the opening. Firstplunger 320A is used to compact (for example, by applying mechanicaland/or hydraulic force to the top of the plunger) electricallyinsulating material inside device 316. For example, force may be appliedto first plunger 320A using a hammer (mechanical compaction) or ahydraulically driven piston (hydraulic compaction).

FIG. 29 depicts a side view of insulated conductor 212 inside device 316with first plunger 320A in position above the insulated conductor withexposed core 214. In certain embodiments, first plunger 320A has abottom with recess 322A. Recess 322A may have a shape that issubstantially similar to the shape of the exposed portions of the cores.First plunger 320A may include stops 324, shown in FIG. 28, that inhibitthe depth the first plunger can go into device 316. For example, stops324 may inhibit first plunger 320A from going to a depth inside device316 that would bend or deform the cores of the insulated conductors. Insome embodiments, first plunger 320A is designed to go to a selecteddepth that does not bend or deform the cores of the insulated conductorswithout the use of stops (for example, the top plate of the plunger actsas the stop).

First plunger 320A may be used to compact electrically insulatingmaterial 256 to a first level inside device 316. For example, as shownin FIG. 29, electrically insulating material 256 is compacted to levelthat surrounds a lower portion (for example, a lower half) of exposedcore 214. The process of adding electrically insulating material andcompacting the material with the first plunger may be repeated until adesired level of compaction is achieved around a lower portion of thecore.

FIG. 30 depicts a side view of insulated conductor 212 inside device 316with second plunger 320B in position above the insulated conductor withexposed core 214. In certain embodiments, second plunger 320B has abottom with recess 322B. Recess 322B may have a shape that issubstantially similar to the outer shape of the insulated conductor.

In some embodiments, recess 322B in second plunger 320B has other shapesor there is no recess. FIGS. 31A-D depict other embodiments of secondplunger 320B. In FIG. 31A, second plunger 320B has no recess. In FIG.31B, recess 322B has 30° angled edges. In FIG. 31C, recess 322B has 15°angled straight edges. In FIG. 31D, recess 322B is slightly shallower(shorter sides) than the recess shown in FIG. 30.

Second plunger 320B may be used to compact electrically insulatingmaterial 256 to a second level inside device 316. For example, as shownin FIG. 30, electrically insulating material 256 is compacted to levelthat surrounds exposed core 214. The process of adding electricallyinsulating material and compacting the material with the second plungermay be repeated until a desired level of compaction is achieved aroundthe core. For example, the process may be repeated until the desiredlevel of compaction of electrically insulating material is achieved in ashape and outside diameter similar to the shape and outside diameter ofthe insulated conductor.

After compaction of a desired amount of electrically insulatingmaterial, device 316 may be removed from around the coupling of theinsulated conductors. FIG. 32 depicts an embodiment with the second halfof device 316 removed to leave first half 316A and electricallyinsulating material 256 compacted around the coupling between insulatedconductors 212A, 212B.

After removal of device 316, compacted electrically insulating material256 may be shaped into a substantially cylindrical shape with theoutside diameter relatively similar to the outside diameter of insulatedconductors 212A, 212B, as shown in FIG. 33. Compacted electricallyinsulating material 256 may be formed into its final shape by removingexcess portions of the compacted material. For example, excess portionsof compacted electrically insulating material 256 may be axially removedusing a saw blade, a sleeve with a shaving edge slid over the compactedmaterial, and/or other techniques known in the art.

After electrically insulating material 256 is formed into the finalshape, sleeve 252 is placed over the electrically insulating material,as shown in FIG. 34. Sleeve 252 may include two or more portions placedover the electrically insulating material and coupled (welded) togetherto form the sleeve. In some embodiments, the two or more portions ofsleeve 252 are compressed using a pressurized fluid inside an outersleeve (such as described in the embodiments of inner sleeve 252A andouter sleeve 252B depicted in FIGS. 24 and 25) and/or by mechanicallycrimping the sleeve portions together (such as described in theembodiments of sleeve 252 depicted in FIGS. 36 and 37). Compressionusing the pressurized fluid and/or mechanically crimping sleeve 252 mayclose gaps between portions of the sleeve such that no weld is needed tojoin the portions together. Additionally, compression using thepressurized fluid and/or mechanically crimping may bring down theinterface (make a tighter interference fit) between sleeve 252 andelectrically insulating material 256. Sleeve 252 may be coupled (welded)to jackets of insulated conductors 212A, 212B. Sleeve 252 may be made ofmaterials similar to the jackets of insulated conductors 212A, 212B. Forexample, sleeve 252 may be 304 stainless steel.

In certain embodiments, electrically insulating material 256 that iscompacted in device 316 includes a mixture of magnesium oxide and boronnitride powders. In an embodiment, electrically insulating material 256that is compacted in device 316 includes an 80% by weight magnesiumoxide, 20% by weight boron nitride powder mixture. Other electricallyinsulating materials and/or other mixtures of electrically insulatingmaterials may also be used. In some embodiments, a combination ofelectrically insulating material powder and blocks of electricallyinsulating material are used.

FIG. 35 depicts a representation of an embodiment of hydraulic pressmachine 426 that may be used to apply force to a plunger tohydraulically compact electrically insulating material inside a device(for example, device 316 depicted in FIGS. 27-32). Hydraulic pressmachine 426 may include piston 428 and device holder 430. In certainembodiments, insulated conductors may be fed through clamps 432 ofhydraulic press machine 426 such that end portions of the insulatedconductors are positioned under piston 428 and above device holder 430.Clamps 432 may be used to secure the ends of the insulated conductors onmachine 426. Positioners 434 may be used to make fine tuning adjustmentsin the positions of the insulated conductors.

A device, such as device 316 depicted in FIGS. 27-32, may be placedaround the ends of the insulated conductors at device holder 430 (forexample, the two halves of the device are put together around the endsof the insulated conductors). Device holder 430 may support the deviceduring compaction of material in the device. During compaction, piston428 may apply force to a plunger (for example, first plunger 320Adepicted in FIGS. 28-29 and/or second plunger 320B depicted in FIG. 30)to compact electrically insulating material around the ends of theinsulated conductors. In some embodiments, piston 428 provides forces ofup to about 50 tons force (about 100,000 pounds force).

Hydraulic compaction of electrically insulating material in device 316,depicted in FIGS. 27-32, may provide compaction levels (for example, upto about 85% compaction) in the electrically insulating material thatare similar to compaction levels in the insulated conductors. Suchcompaction levels will produce splices that are suitable for operatingtemperatures up to at least about 1300° F. (about 700° C.). Hydrauliccompaction of electrically insulating material in device 316 may providemore controlled compaction and/or more repeatable compaction (repeatablefrom splice to splice). Hydraulic compaction may be achieved with lessmovement or variation to provide more even and consistent pressure thanmechanical compaction.

In some embodiments, hydraulic compaction is used in combination withmechanical compaction (for example, the electrically insulating materialis first compacted mechanically and then further compacted usinghydraulic compaction). In some embodiments, the electrically insulatingmaterial is compacted while at elevated temperatures. For example, theelectrically insulating material may be compacted at a temperature ofabout 90° C. or higher. In some embodiments, first plunger 320A and/orsecond plunger 320B are coated with non-stick materials. For example,the plungers may be coated with non-metallic materials such as ceramicsor DLC (Diamond-Like Carbon) coatings available from Morgan TechnicalCeramics (Berkshire, England). Coating the plungers may inhibit metaltransfer into the electrically insulating material and/or sticking ofthe electrically insulating material to the plungers.

In certain embodiments, a sleeve is mechanically compressedcircumferentially around the sleeve to compress the sleeve. FIG. 36depicts an embodiment of sleeve 252 that is used in circumferentialmechanical compression. Sleeve 252 may be placed around blocks and/orpowder of electrically insulating material. For example, sleeve 252 maybe placed around blocks of electrically insulating material depicted inFIG. 23, compacted electrically insulating material powder depicted inFIG. 33, or combinations of the depicted blocks and powder.

In certain embodiments, sleeve 252 includes ribs 326. Ribs 326 may beraised portions of sleeve 252 (for example, high spots on the outerdiameter of the sleeve.). Ribs 326 may be shaped and sized to match thecrimping portions of a press used to mechanically compress sleeve 252.For example, sleeve 252 may be compressed using a hydraulically actuatedmechanical compression system that circumferentially compresses thesleeve circumferentially. For example, sleeve 252 may be compressedusing a Pyplok® swage tool available from Tube-Mac® Industries (StoneyCreek, Ontario, Canada).

Crimping portions of the press compress ribs 326 until the ribs arecompressed to about the outer diameter of the remaining portions ofsleeve 252 (the ribs have a diameter substantially similar to thediameter of the remainder of the sleeve). FIG. 37 depicts an embodimentof sleeve 252 on insulated conductors 212A, 212B after the sleeve andribs 326 have been circumferentially compressed. Compression of ribs 326circumferentially (radially) compresses electrically insulating materialinside sleeve 252 and couples the sleeve to insulated conductors 212A,212B. Sleeve 252 may be further coupled to insulated conductors 212A,212B. For example, the ends of sleeve 252 may be welded to the jacketsof insulated conductors 212A, 212B.

The fittings depicted herein (such as, but not limited to, fitting 250(depicted in FIGS. 5, 7, 18, 19, 20, and 21), fitting 270 (depicted inFIG. 8), fitting 298 (depicted in FIGS. 14,15, and 16), embodiments ofthe fitting formed from inner sleeve 252A and outer sleeve 252B(depicted in FIGS. 22-25), and embodiments of sleeve 252 (depicted inFIGS. 34, 36, and 37) may form robust electrical and mechanicalconnections between insulated conductors. For example, fittings depictedherein may be suitable for extended operation at voltages above 1000volts, above 1500 volts, or above 2000 volts and temperatures of atleast about 650° C., at least about 700° C., at least about 800° C.

In certain embodiments, the fittings depicted herein couple insulatedconductors used for heating (for example, insulated conductors locatedin a hydrocarbon containing layer) to insulated conductors not used forheating (for example, insulated conductors used in overburden sectionsof the formation). The heating insulated conductor may have a smallercore and different material core than the non-heating insulatedconductor. For example, the core of the heating insulated conductor maybe a copper-nickel alloy, stainless steel, or carbon steel while thecore of the non-heating insulated conductor may be copper. Because ofthe difference in sizes and electrical properties of materials of thecores, however, the electrical insulation in the sections may havesufficiently different thicknesses that cannot be compensated in asingle fitting joining the insulated conductors. Thus, in someembodiments, a short section of intermediate heating insulated conductormay be used in between the heating insulated conductor and thenon-heating insulated conductor.

The intermediate heating insulated conductor may have a core diameterthat tapers from the core diameter of the non-heating insulatedconductor to the core diameter of the heating insulated conductor whileusing core material similar to the non-heating insulated conductor. Forexample, the intermediate heating insulated conductor may be copper witha core diameter that tapers to the same diameter as the heatinginsulated conductor. Thus, the thickness of the electrical insulation atthe fitting coupling the intermediate insulated conductor and theheating insulated conductor is similar to the thickness of theelectrical insulation in the heating insulated conductor. Having thesame thickness allows the insulated conductors to be easily joined inthe fitting. The intermediate heating insulated conductor may providesome voltage drop and some heating losses because of the smaller corediameter, however, the intermediate heating insulated conductor may berelatively short in length such that these losses are minimal.

In certain embodiments, a fitting for joining insulated conductors iscompacted or compressed to improve the electrical insulation properties(dielectric characteristics) of electrically insulating material insidethe fitting. For example, compaction of electrically insulating materialinside the fitting may increase the uniformity of the electricallyinsulating material and/or remove voids or other interfaces in theelectrically insulating material.

In some embodiments, blocks of electrically insulating material (forexample, magnesium oxide) are compacted in the fitting. In someembodiments, electrically insulating material powder is compacted in thefitting. In some embodiments, combinations of powder and/or blocks ofelectrically insulating material are used in the fitting. In addition,combinations of different types of electrically insulating material maybe used (for example, a combination of magnesium oxide and boronnitride).

In embodiments described herein that use electrically insulatingmaterial powder, the powder has selected properties that provide forbetter compaction (higher density when compacted). In some embodiments,the powder has a selected particle size distribution (for example, thesize distribution may average between about 100 μm and about 200 μm formagnesium oxide powder). A desired range may be selected such that thepowder compacts to a desired density. Other properties of the powderthat may be selected to provide a desired density under compactioninclude, but are not limited to, particle shape, impurity properties(for example, ratios of impurities such as silicon or calcium), wallfriction properties (wall friction angle), compactibility understandardized force (compaction in a standard size cylinder under thesame force), and hopper angle to achieve mass flow in a hopper. Thecombination of one or more of these properties may be indicators thecompactibility of the powder and/or the ability of the powder to flowduring compression or compaction.

A fitting used to join insulated conductors may be compactedmechanically, pneumatically, and/or hydraulically. Compaction of thefitting may improve the dielectric characteristics of the electricallyinsulating material such that the electrically insulating material hasdielectric characteristics that are similar to the dielectriccharacteristics of electrical insulation in the insulated conductors. Insome embodiments, compacted electrically insulating material in thefitting may have dielectric characteristics that are better than thedielectric characteristics of electrical insulation in the insulatedconductors.

As an example, electrical insulation (magnesium oxide) in an insulatedconductor typically has a density of between about 78% and about 82%.Uncompacted magnesium oxide powder may have a density of between about50% and about 55%. Magnesium oxide blocks may have a density of about70%. In certain embodiments of fittings described herein, the electricalinsulation inside the fitting after compaction or compression has adensity that is at least within about 15%, within about 10%, or withinabout 5% of the density of the insulated conductors coupled to thefitting. In some embodiments described herein, the electrical insulationinside the fitting after compaction or compression has a higher densitythan the density of the insulated conductors coupled to the fitting. Forexample, the electrical insulation inside the fitting may have a densityup to about 85%.

In certain embodiments described herein, a reinforcement sleeve or otherstrain relief is placed at or near the coupling of insulated conductors.FIG. 38 depicts an embodiment of reinforcement sleeves 328 on joinedinsulated conductors 212A, 212B. Reinforcement sleeves 328 providestrain relief to strengthen the coupling between the insulatedconductors. Reinforcement sleeves 328 allow the joined insulatedconductors to be spooled, unspooled, and pulled in tension forinstallation/removal in wellbores and/or in an installation conduit (forexample, coiled tubing installation).

FIG. 39 depicts an exploded view of another embodiment of fitting 270used for coupling three insulated conductors 212A, 212B, 212C. Incertain embodiments, fitting 270 includes strain relief fitting 274,electrical bus 330, cylinder 332, and end cap 272. FIGS. 40-47 depict anembodiment of a method for installation of fitting 270 onto ends ofinsulated conductors 212A, 212B, 212C.

In FIG. 40, insulated conductors 212A, 212B, 212C are passed throughlongitudinal openings in strain relief fitting 274. Strain relieffitting 274 may be an end termination for insulated conductors 212A,212B, 212C. After installation of insulated conductors 212A, 212B, 212Cinto strain relief fitting 274, insulated conductors 212A, 212B, 212Care aligned in the strain relief fitting and a portion of cores 214A,214B, 214C protruding from the fitting are exposed. Cores 214A, 214B,214C are exposed by removing end portions of the jackets and electricalinsulators of insulated conductors 212A, 212B, 212C that extend throughstrain relief fitting 274.

In certain embodiments, end portions of cores 214A, 214B, 214C extendingthrough strain relief fitting 274 are brazed to the strain relieffitting. Examples of materials for brazing include, but are not limitedto, nickel brazes such as AWS 5.8 BNi-2 for low sulfur environments andAWS 5.8 BNi-5A for high sulfur environments. The brazing material mayflow during brazing and fill and seal any gaps between cores 214A, 214B,214C and strain relief fitting 274. Sealing the gaps prevent fluids fromflowing into the inside of fitting 270. Brazing end portions of cores214A, 214B, 214C to strain relief fitting 274 may allow for the cores tobe spaced closer together and reduce the size of the strain relieffitting. Having a smaller strain relief fitting 274 may allow fitting270 and the wellbore for the heater to be smaller in diameter astypically the end termination (fitting 270) is the determining factor inwellbore size. In some embodiments, the jackets of insulated conductors212A, 212B, 212C are coupled to strain relief fitting 274. For example,the jackets may be welded (seam welded) to strain relief fitting 274.

In FIG. 41, first cylinder 332A is coupled to the end of strain relieffitting 274 with protruding cores 214A, 214B, 214C. First cylinder 332Amay be welded into place on the end of strain relief fitting 274. Firstcylinder 332A may have a longitudinal length less than the length ofprotruding cores 214A, 214B, 214C. Thus, at least some portion of thecores may extend beyond the length of first cylinder 332A.

Following coupling of first cylinder 332A to strain relief fitting 274,electrically insulating material 256 is added into the cylinder to atleast partially cover cores 214A, 214B, 214C, as shown in FIG. 42. Thus,at least a portion of the cores remain exposed above electricallyinsulating material 256. Electrically insulating material 256 mayinclude powder and/or blocks of electrically insulating material (forexample, magnesium oxide). In certain embodiments, electricallyinsulating material 256 is compacted inside first cylinder 332A.Electrically insulating material 256 may be hydraulically and/ormechanically compacted using a compaction tool. For example, force maybe applied to the compaction tool using a piston of a hydrauliccompaction machine. FIG. 48 depicts an embodiment of compaction tool334A that can be used to compact electrically insulating material 256.Compaction tool 334A may have openings that allow the tool to fit overcores 214A, 214B, 214C while compacting electrically insulatingmaterial. After compaction in the above step and later described steps,the surface of electrically insulating material 256 may be scarred.Scarring the surface of electrically insulating material 256 promotesbonding between layers of electrically insulating material duringcompaction of the layers.

In certain embodiments, after compaction of electrically insulatingmaterial 256 in cylinder 332A, the portion cores 214A, 214B, 214C thatremain exposed are coupled to electrical bus 330, as shown in FIG. 43.Electrical bus 330 may be, for example, copper or another materialsuitable for electrically coupling cores 214A, 214B, 214C together. Insome embodiments, electrical bus 330 is welded to cores 214A, 214B,214C.

After coupling electrical bus 330 to cores 214A, 214B, 214C, secondcylinder 332B may be coupled to first cylinder 332A to form cylinder 332around the exposed portions of the cores, as shown in FIG. 44. In someembodiments, cylinder 332 is a single cylinder coupled to strain relieffitting 274 in a single step. In some embodiments, cylinder 332 includestwo or more cylinders coupled to strain relief fitting 274 in multiplesteps.

Second cylinder 332B may be welded into place on the end first cylinder332A. As shown in FIG. 44, completed cylinder 332 may have alongitudinal length that extends beyond the length of protruding cores214A, 214B, 214C. Thus, the cores may are contained within theboundaries of cylinder 332.

Following formation of cylinder 332, electrically insulating material256 is added into the cylinder to a level that is about even with thetop of cores 214A, 214B, 214C and electrical bus 330, as shown in FIG.45. In certain embodiments, electrically insulating material 256 at thelevel shown in FIG. 45 is compacted (for example, mechanicallycompacted). FIG. 49 depicts an embodiment of compaction tool 334B thatcan be used to compact electrically insulating material 256. Compactiontool 334B may have an annulus that allows the tool to fit overelectrical bus 330 and cores 214A, 214B, 214C while compactingelectrically insulating material.

Following compaction of material at the level of the top of electricalbus 330 and cores 214A, 214B, 214C, additional electrically insulatingmaterial 256 is added into the cylinder to completely cover theelectrical bus and the cores, as shown in FIG. 46. Thus, the cores andelectrical bus are substantially enclosed in electrically insulatingmaterial 256. In certain embodiments, electrically insulating material256 added into cylinder 332 to enclose the cores is compacted (forexample, mechanically compacted). FIG. 50 depicts an embodiment ofcompaction tool 334C that can be used for the final compaction ofelectrically insulating material 256.

After final compaction of electrically insulating material 256, end cap272 is coupled (welded) to cylinder 332 to form fitting 270. In someembodiments, end cap 272 is shaped to be used as a guide for guiding theinstallation of insulated conductors 212A, 212B, 212C into a wellbore ora deployment device (for example, coiled tubing installation). In someembodiments, fitting 270 is used with insulated conductors operating assingle phase heaters. For example, fitting 270 may be used with twoinsulated conductors coupled in a hairpin configuration with theinsulated conductors coupled inside the fitting to have one insulatedconductor as the supply conductor and one as the return conductor.Fitting 270 may also be used with one insulated conductor that uses thejacket of the insulated conductor to return current to the surface ofthe formation.

Mechanical compaction of electrically insulating material inside fitting270 may produce a fitting with a higher mechanical breakdown voltageand/or operating temperature than fittings that are filled withelectrically insulating material and vibrated for compaction of theelectrically insulating material. For example, fitting 270 may beoperable at voltages above about 6 kV and temperatures above about 1300°F. (about 700° C.). Because fitting 270 (the heater end termination) isoperable at temperatures above about 700° C., the fitting may be usablein heated layers of a subsurface formation (for example, layersundergoing pyrolyzation). Thus, the end of a heater does not have to beplaced in a cooler portion of the formation and the heater wellbore maynot need to be drilled as deep into the formation or into differenttypes of formation.

In certain embodiments, a failed three-phase heater is converted tosingle-phase operation using the same power supply. If, for example, oneleg of a three-phase heater fails (ground-faults), the remaining twolegs of the heater can be used as a single-phase heater with one legbeing the supply conductor and the other leg being the return conductor.To convert the heater to single-phase operation, a high impedanceresistor may be put between the neutral of the three-phase power supply(transformer) and the ground-faulted leg of the heater. The resistor isput in series with the ground-faulted leg of the heater. Because of thehigh resistance of the resistor, voltage is taken off the ground-faultedleg and put across the resistor. Thus, the resistor is used todisconnect power to the ground-faulted leg with little or no currentpassing through the ground-faulted leg. After the resistor is putbetween the neutral of the transformer and the ground-faulted leg, theremaining two legs of the heater operate in a single-phase mode withcurrent going down one leg, passing through an end termination, andreturning up the other leg.

During three-phase operation of the heater, the voltage at the endtermination is near zero as the three legs operate 120° out of phase tobalance the voltages between the three legs (voltage may not be exactlyzero if there is any misbalance between the legs in the circuit). Theend termination is typically isolated from ground for the three-phaseheater. When the heater is converted to single-phase, the voltage on theend termination increases from the near zero voltage to about half theoutput voltage of the power supply. The voltage on the end terminationincreases during single-phase operation as current now passes linearlythrough the two operating legs with the end termination being at thehalfway point of the circuit. As an example, during three-phaseoperation with a 480V power supply, each leg may be at about 277 V withabout 0 V at the end termination at the bottom of the heater. Afterconversion to single-phase operation with the resistor in series withthe ground-faulted leg, the legs operating in single-phase produce avoltage of about 240V at the end termination at the bottom of theheater.

Because voltages for heating subsurface or hydrocarbon containingformations to mobilization and/or pyrolyzation temperatures aretypically very high due to the long lengths of the heaters (for example,about 1 kV or higher), the end termination needs to be able to operateat even higher voltages to be used for single-phase operation. Currentend terminations used in subsurface heating are not typically operableat such high voltages. Because fitting 270, however, is operable atvoltages above 6 kV, fitting 270 allows a failed high voltagethree-phase subsurface heater to be converted to a single-phaseoperation.

EXAMPLES

Non-restrictive examples are set forth below.

Samples Using Fitting Embodiment Depicted in FIG. 5

Samples using an embodiment of fitting 250 similar to the embodimentdepicted in FIG. 5 were fabricated using a hydraulic compaction machinewith a medium voltage insulated conductor suitable for use as asubsurface heater on one side of the fitting and a medium voltageinsulated conductor suitable for use as an overburden cable on the otherside of the fitting. Magnesium oxide was used as the electricallyinsulating material in the fittings. The samples were 6 feet long fromthe end of one mineral insulated conductor to the other. Prior toelectrical testing, the samples were placed in a 6½ ft long oven anddried at 850° F. for 30 hours. Upon cooling to 150° F., the ends of themineral insulated conductors were sealed using epoxy. The samples werethen placed in an oven 3 feet long to heat up the samples and voltagewas applied to the samples using a 5 kV (max) hipot (high potential)tester, which was able to measure both total and real components of theleakage current. Three thermocouples were placed on the samples andaveraged for temperature measurement. The samples were placed in theoven with the fitting at the center of the oven. Ambient DC (directcurrent) responses and AC (alternating current) leakage currents weremeasured using the hipot tester.

A total of eight samples were tested at about 1000° F. and voltages upto 5 kV. One individual sample tested at 5 kV had a leakage current of2.28 mA, and another had a leakage current of 6.16 mA. Three moresamples with cores connected together in parallel were tested to 5 kVand had an aggregate leakage current of 11.7 mA, or 3.9 mA averageleakage current per cable, and the three samples were stable. Threeother samples with cores connected together in parallel were tested to4.4 kV and had an aggregate leakage current of 4.39 mA, but they couldnot withstand a higher voltage without tripping the hipot tester (whichoccurs when leakage current exceeds 40 mA). One of the samples tested to5 kV underwent further testing at ambient temperature to breakdown.Breakdown occurred at 11 kV.

A total of eleven more samples were fabricated for additional breakdowntesting at ambient temperature. Three of the samples had insulatedconductors prepared with the mineral insulation cut perpendicular to thejacket while the eight other samples had insulated conductors preparedwith the mineral insulation cut at a 30° angle to the jacket. Of thefirst three samples with the perpendicular cut, the first samplewithstood up to 10.5 kV before breakdown, the second sample withstood upto 8 kV before breakdown, while the third sample withstood only 500 Vbefore breakdown, which suggested a flaw in fabrication of the thirdsample. Of the eight samples with the 30° cut, two samples withstood upto 10 kV before breakdown, three samples withstood between 8 kV and 9.5kV before breakdown, and three samples withstood no voltage or less than750 V, which suggested flaws in fabrication of these three samples.

Samples Using Fitting Embodiment Depicted in FIG. 8b

Three samples using an embodiment of fitting 270 similar to theembodiment depicted in FIG. 8B were made. The samples were made with twoinsulated conductors instead of three and were tested to breakdown atambient temperature. One sample withstood 5 kV before breakdown, asecond sample withstood 4.5 kV before breakdown, and a third samplecould withstand only 500 V, which suggested a flaw in fabrication.

Samples Using Fitting Embodiment Depicted in FIGS. 14 and 15

Samples using an embodiment of fitting 298 similar to the embodimentdepicted in FIGS. 14 and 15 were used to connect two insulatedconductors with 1.2″ outside diameters and 0.7″ diameter cores. MgOpowder (Muscle Shoals Minerals, Greenville, Tenn., U.S.A.) was used asthe electrically insulating material. The fitting was made from 347Hstainless steel tubing and had an outside diameter of 1.5″ with a wallthickness of 0.125″ and a length of 7.0″. The samples were placed in anoven and heated to 1050° F. and cycled through voltages of up to 3.4 kV.The samples were found to viable at all the voltages but could notwithstand higher voltages without tripping the hipot tester.

In a second test, samples similar to the ones described above weresubjected to a low cycle fatigue-bending test and then testedelectrically in the oven. These samples were placed in the oven andheated to 1050° F. and cycled through voltages of 350 V, 600 V, 800 V,1000 V, 1200 V, 1400 V, 1600 V, 1900 V, 2200 V, and 2500 V. Leakagecurrent magnitude and stability in the samples were acceptable up tovoltages of 1900 V. Increases in the operating range of the fitting maybe feasible using further electric field intensity reduction methodssuch as tapered, smoothed, or rounded edges in the fitting or addingelectric field stress reducers inside the fitting.

It is to be understood the invention is not limited to particularsystems described which may, of course, vary. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only, and is not intended to belimiting. As used in this specification, the singular forms “a”, “an”and “the” include plural referents unless the content clearly indicatesotherwise. Thus, for example, reference to “a core” includes acombination of two or more cores and reference to “a material” includesmixtures of materials.

In this patent, certain U.S. patents, U.S. patent applications, andother materials (for example, articles) have been incorporated byreference. The text of such U.S. patents, U.S. patent applications, andother materials is, however, only incorporated by reference to theextent that no conflict exists between such text and the otherstatements and drawings set forth herein. In the event of such conflict,then any such conflicting text in such incorporated by reference U.S.patents, U.S. patent applications, and other materials is specificallynot incorporated by reference in this patent.

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements described herein withoutdeparting from the spirit and scope of the invention as described in thefollowing claims.

1-94. (canceled)
 95. A method for coupling ends of two insulatedconductors, comprising: coupling an end portion of a core of a firstinsulated conductor to an end portion of a core of a second insulatedconductor, wherein at least a part of the end portions of the cores areat least partially exposed; placing electrically insulating materialover the exposed portions of the cores; placing a sleeve over endportions of the two insulated conductors to be coupled, the sleevecomprising one or more raised portions, wherein the end portions of thetwo insulated conductors comprise the exposed portions of the cores;coupling the sleeve to jackets of the insulated conductors; andmechanically compressing the raised portions of the sleeve until theraised portions of the sleeve have a diameter substantially similar to aremainder of the sleeve, wherein the compression of the raised portionsof the sleeve compacts the electrically insulating material inside thesleeve.
 96. The method of claim 95, wherein mechanically compressing theraised portions of the sleeve comprises radially compressing the raisedportions.
 97. The method of claim 95, wherein the sleeve has a lengthand is positioned such that the length of the sleeve substantiallymatches the gap between non-exposed portions of the insulatedconductors.
 98. The method of claim 95, wherein at least one of theinsulated conductors comprises a core at least partially surrounded byan electrical insulator and an outer jacket, the outer jacket at leastpartially surrounding the electrical insulator.
 99. The method of claim95, further comprising exposing the core of at least one of theinsulated conductors by removing a portion of an electrical insulatorand an outer jacket surrounding the core at an end of at least one ofthe insulated conductors.
 100. The method of claim 95, wherein theelectrically insulating material comprises blocks of electricallyinsulating material and/or electrically insulating material powder. 101.The method of claim 95, wherein the electrically insulating materialcomprises blocks of electrically insulating material that have innersurfaces shaped to match the outer surfaces of the end portions of theat least partially exposed cores.
 102. The method of claim 95, furthercomprising coupling one or more strain relief sleeves to at least one ofthe insulated conductors at or near the outer sleeve.
 103. The method ofclaim 95, wherein the sleeve is welded to the jackets of the insulatedconductors.
 104. The method of claim 95, further comprising providingpressure on the sleeve to further compress the sleeve into the compactedpowder material and further compact the powder material.
 105. The methodof claim 95, further comprising forming at least one chamfer on the endportion of at least one of the insulated conductors.
 106. The method ofclaim 95, further comprising compacting the electrically insulatingmaterial inside the sleeve such that the electrically insulatingmaterial has a density that is at least within about 15% of the densityof at least one of the insulated conductors. 107-138. (canceled)